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COFYI«GHT DEPOSm 



PRINCIPLES 

OF 

ENGINEERING DRAWING 



FOR 



TECHNICAL STUDENTS 



BY 



CHARLES C. LEEDS, B.S. 

PROFESSOR OF MECHANICAL DRAWING, 
CARNEGIE INSTITUTE OF TECHNOLOGY 



105 Illustrations 




NEW YORK 

D. VAN NOSTRAND COMPANY 

25 Park Place 

1919 



T/ 



.u 



COPYRIGHT, 1919 
D. VAN NOSTRA ND COMPANY 



NOV -5 i919 



©CI.A536441 



TO THE 

OHIO MECHANICS INSTITUTE 

THE ALMA MATER WHO HAS HELPED SO MANY CINCINNATI 

BOYS TO GAIN A TECHNICAL TRAINING, THIS VOLUME 

IS GRATEFULLY DEDICATED BY ONE OF HER SONS 



PREFACE 

The subject matter of this text has been carefully 
prepared and arranged with a view to meeting the 
needs of Freshman students in Engineering Schools 
and Colleges. It contains, in addition, ample material 
for the requirements of more advanced men who are 
interested in Engineering Drawing. 

The ability to use engineering drawings intelUgently 
presupposes the power to make mental translations 
from orthographic projection drawings into perspec- 
tive, and from perspective back to orthographic, as 
these processes are constantly taking place in the vari- 
ous departments of manufacturing plants engaged in 
engineering construction. 

Under the theory that as a boy grows up he develops 
a natural tendency to visualize objects in perspective 
form, the author has made use of angular perspective 
as a means of introducing the subject of orthographic 
projection, believing that a sound grasp of the latter 
subject miay be obtained by comparing it with a known 
subject. 

After the fundamentals of both perspective and or- 
thographic have been studied thoroughly, we apply 
this instruction immediately when taking up freehand 
sketching, for here the student is required to use his 
reasoning faculties to translate perspective sketches 
into freehand orthographic projection drawings. 

For certain other problems given in this same chapter, 
the student is obliged to make his sketches from a 
written description of the objects which form the sub- 



vi PREFACE 

ject matter of his drawings. Both of these methods 
of presentation, i.e., translation and written descrip- 
tion, are valuable aids in developing the student's 
power to visualize inentally, both perspective pictures 
and the various orthographic views as well. The 
translation method is followed later when taking up 
isometric projection, as the problems are shown in the 
form of orthographic sketches from which the student 
is required to lay out his drawing of each object in 
isometric. 

The primary aim in presenting these various prob- 
lems in this fashion, is to enable the student to under- 
stand drawings readily, and to give him the ability to 
make mental translations quickly when objects are 
presented by either method, and thus to give the stu- 
dent confidence in his understanding of this vital fea- 
ture of engineering drawing. 

We have led up to the subject of ^Svorking drawings" 
by giving the student a thorough grounding in the 
technical methods followed in the production of these 
drawings; consequently, from this period on, it is 
largely a matter of applying these methods with intel- 
ligence in order to produce the creative draftsman. 

The author desires to express his appreciation for the 
helpful suggestions given during the preparation of this 
text by Professors C. W. Sproull and H. L. McKee. 
He also wishes to acknowledge his obligation to Mr. 
W. A. Emery for his valuable assistance in the prepa- 
ration of the various drawings. 



CONTENTS 

PAGE 

CHAPTER I 
Purpose of Instruction 1 

CHAPTER II 

Drawing Instruments and Methods of Handling 4 

Pencils. — Paper. — Board, T Square and Triangles. — Scale. 

— Instruments, preparation and modes of handling. — Practice 
Problems to familiarize students with use of tools. 

CHAPTER III 

Lettering and Figures 19 

Proportions and method of construction. — Examples. — Prob- 
lems in pencil lettering. 

CHAPTER IV 

Elementary Perspective 24 

Angular Perspective. — Picture Plane. — Phenomena of Per- 
spective. — • Vanishing Points. — Station Point. — Horizon, 
etc. — ■ Perspective Scale. — Cube. — ■ Circle Construction. — 
Problems in 45° Perspective. 

CHAPTER V 

Orthographic Projection 33 

Orthographic compared with Perspective. — Planes of Pro- 
jection. — Revolution of Planes. — ■ Relationship of Views. — - 
Arrangement of Views. — Auxiliary Planes. 

CHAPTER VI 

Freehand Sketching 40 

Use of Sketches. — Short Stroke Method. — Suggestions. — 
Proportions. — Problems. — Translation from Orthographic to 
Perspective, Translation from Perspective to Orthographic. — 
Sketching from written description. 

CHAPTER VII 

Engineering Curves 47 

The Ellipse Construction. — ■ Generating the Path of a Moving 
Point. — Cycloid. — Epicycloid. — Hypocycloid. — Involute. 

— Helix. 

vii 



viii CONTENTS 

CHAPTER VIII 

Conic Sections. — Intersections and Developments 54 

Conic Sections. — • Intersection of Cylinders. — Parallel Line 
Development. — Intersection of Cone and Cylinder. — Radial 
Line Development. — Triangulation Development. — Prob- 
lems. 

CHAPTER IX 

Isometric and Oblique Drawing 64 

Isometric Projection. — Isometric Axes. — Coordinate Axes. 

— Circles. — Oblique Drawing. — Cabinet Drawing. — - Prob- 
lems. — Translation from Orthographic to Isometric and 
Oblique. 

CHAPTER X 

Drafting Room Conventions 78 

Lines. — Screw Threads. — Fasteners, Bolts, Screws, Keys, Set 
Screws, Nuts. — Breaks. — Sectioning, True and Conventional 
Sections. — Dimensions. ^ Standard Data. — Composite Draw- 
ing. — Abbreviations. — Bill of Material. — Reverse Curves. 

— Checking. 

CHAPTER XI 

Working Drawings 102 

Detail and Assembly Drawings. — Scale. — • Titles. — Problems, 
Detail Drawings of Clamp, Shaft Support, Tool Rest, Pulley, 
Hand Wheel, Jack, Couplings, Complete Detail and Assembly 
Drawings of Speed Lathe. 

CHAPTER XII 

Tracing and Blue Printing 120 

Method of handhng pen. — Tracing Cloth. — Tracing Methods. 
— • General Notes. — Blue Print Paper. — Printing. — Xan 
Dyke Prints. 

CHAPTER XIII 

Reference Tables 129 

U. S. Std. Screw Threads. — U. S. Standard Bolt and Nut 
Sizes, Washers. — Cap Screws. — Machine Screws. — Decimal 
Equivalents. — Standard Rivets. — Taper Keys, Woodruff 
Keys. — Taper Pins. — Standard Pipe Sizes. — Standard 
Wire Gages. 



PEINCTPLES OF ENGINEERING 
DRAWING FOR TECHNICAL STUDENTS 

CHAPTER I 

PURPOSE OF INSTRUCTION 

A STUDY of drawing as applied to the various 
forms of engineering construction is of decided 
importance to all students of technology. This 
subject has both educational and practical value of 
a high order, and the beginner should approach 
the study of drawing with a full appreciation of 
this fact, if he is to profit fully from his efforts. 

There are few, if any, subjects of instruction 
so helpful in stimulating the reasoning faculties as 
a careful study of engineering drawing, and there 
is no subject of equal value for training the powers 
of accurate perception. Engineering drawing is a 
fundamental tool constantly used in developing 
the growth of ideas born of the creative imagination, 
a faculty vitally essential to success in the engineer- 
ing field. 

The name Engineering Drawing covers the various 
forms of drawing used in engineering construction; 
of these the most important are mechanical and 
freehand drawing. 

Technically, a mechanical drawing is a drawing 
made with instruments; actually, in the manu- 
facturing and engineering world, it is an instrument 



2 PRINCIPLES OF ENGINEERING DRAWING 

or device for conveying exact information from one 
person to another. It is a graphic illustration of 
some mechanism or form of construction, a com- 
mercial necessity which is preliminary to all forms 
of engineering construction. 

An engineering drawing represents the written 
form of a Language. This language may be de- 
scribed as a ^' pictorial " one, as it is by means of 
a drawing showing one or more views of an object 
that we furnish the necessary information as to the 
shape and the size of this object. 

To be able to clearly understand engineering 
drawings we must learn to read and write this 
language by the methods in use in commercial life. 
This means that we must become familiar with the 
principles upon which the subject is founded. 

In beginning the study of drawing, the student 
should bear in mind the fact that all the funda- 
mentals of the subject are of importance, and that 
an understanding of these elements may be obtained 
only through mental and physical effort. Where 
the major emphasis is laid upon physical effort, 
the student is apt to get the impression that the 
important feature is to get drawings finished, rather 
than how they are finished. Manual skill is very 
desirable, and for draftsmen it is a necessity, but a clear 
understanding, based upon reasoned study of the 
subject matter covered, is infinitel}^ more to be de- 
sired; for, without this understanding, original cre- 
ative work is a practical impossibility. 

The most desirable combination is where the 
student studies his drawing problems and makes a 



PURPOSE OF INSTRUCTION 3 

persistent effort to reason them out, and also per- 
forms the physical part of his labors with care, 
neatness, and accuracy. Each time the student 
seriously attempts to reason out a problem, he is 
strengthening and developing those faculties which 
are vitally essential to his success in commercial 
life. 

Whoever plans or performs creative w^ork, such 
as designing some form of engineering construction, 
must have developed his imagination until this 
creative faculty enables him to visualize or form 
mental images of the mechanism which he is plan- 
ning, which creation he transmits to others by means 
of freehand sketches or mechanical drawings. As 
a consequence it is highly desirable for the student 
to attempt from the very beginning to form mental 
pictures of the objects used as subject matter for 
his drawings, and thus to work toward the devel- 
opment of the creative imagination. 



CHAPTER II 
DRAWING TOOLS AND METHODS OF HANDLING 

Mechanical drawings, as the name indicates, 
are made mechanically; that is, with instruments, 
as distinguished from drawings made freehand. 

When taking up the study of mechanical drawing 
it will be greatly to the student's advantage to 
obtain a drawing outfit of good quaUty, for with 
proper care many of the tools A\dll last a life time. 
Another reason for taking good care of the various 
tools is, that it is easier to do work of an excellent 
quahty when the tools are kept in the proper con- 
dition. In general, it will be found that the care- 
ful, accurate draftsman is one who has formed the 
habit of keeping all of his outfit in good working 
order. 

Pencils. - — No tool is more used in makir^g draw- 
ings than a lead pencil, and yet many students 
show a tendency to grow careless in regard to keep- 
ing them properly sharpened. Pencils for drawing 
are made of various degrees of hardness to suit the 
purposes for which they are to be used. Possibh" 
the commonest method of indicating the degree of 
hardness is by placing a numeral before the letter 
H, as 2H, 3H, 4H, etc.; the harder the pencil, the 
higher the number preceding the H. 

For sketching, or printing notes on drawings, H or 
2H pencils are very satisfactory and should be sharp- 



DRAWING TOOLS AND METHODS OF HANDLING 5 

ened, with a round point, as indicated in Fig. 1, 
though the point should not be made as sharp as 
for the drawing pencil. 

The pencil used for making mechanical drawings 
must be of a fairly hard quality to enable one to 





Fig. 1 

maintain a good point for a reasonable length of 
time. For drawing on the common Manila papers, 
pencils of from 4H to 6H will be found entirely 
satisfactory, and it is recommended that one end 
of the drawing (or hard) pencil be sharpened as 
shown in Fig. 1, with a round point, and the other 
end as in Fig. 2, with a flat point. 

Round Point. — This point is produced by first 





Fig. 2 

cutting away the wood, as shown in the illustration. 
Fig. 1, and then sharpening the lead on a smooth 
single-cut file. About one inch from the end of 
the pencil, beginning on one of the six corners, 
cut away the wood in a clean manner so as to bare 
about I inch of the lead; then sharpen it on the file 
by drawing it towards you. Turn the pencil slowly 



6 PRINCIPLES OF ENGINEERING DRAWING 

away from you, taking a fresh hold with each stroke, 
so as to keep the pencil turning on its axis as it is 
moved along the file. 

Flat Point. — The flat point is very useful when it 
is desired to draw very fine, accurate lines, such as 
center lines, construction lines, etc. In sharp- 
ening the fiat point, enter the knife about one inch 
from the end of the pencil on one of the fiat sides 
(not corner) and cut .away the wood in the manner 
shown in the illustration, Fig. 2, baring about one- 
half inch of the lead. To sharpen the lead, slide 
it back and forth along the file, forming a long 
chisel-like point. The fiat side of the lead should 
parallel the fiat side of the pencil when the point 
is finished. 

Paper. — The drawing paper commonly used in 
commercial drafting rooms is known as Manila 
paper. There are a great many grades of this paper 
manufactured, but the main points necessary to 
keep in mind when making a selection are: color, 
erasing qualities and toughness of fibre. 

Commercial drafting rooms usually have three or 
four standard size sheets upon which all of their 
drawings are made; these sizes being dependent 
upon the product of the firm. The following sizes 
are suggested as they have been found very satis- 
factory and they may be cut from a roll with no 
waste: A sheet 22 inches x 30 inches, B sheet 15 
inches x 22 inches, and C sheet 11 inches x 15 inches. 

Drawing paper should be fastened to the board as 
smoothly as possible; for it is very difficult to make 
an accurate drawing on paper which does not lie 




DRAWING TOOLS AND METHODS OF HANDLING 7 

flat on the board. The method of mounting paj^er, 
shown in the illustration, Fig. 3, needs very little 
explanation, and if the student follows the directions 
with reasonable care, the result will be entirely 
satisfactory. Place the tacks in 
the order numbered, stretching 
the paper in the direction indi- 
cated by the arrows. Push the 
tacks well down so that the heads 
bind the paper closely; this will ^ 
also enable the T square to slip 

over them easily without knocking small chips out of 
the edge of the blade. 

Erasers. — For erasing pencil hnes on Manila 
paper the Ruby No. 112 is excellent though the 
Emerald No. Ill is about as satisfactory. For 
cleaning pencil lines or dirt from tracings, both of 
these erasers are rather hard and it is preferable to 
use some of the softer erasers for this purpose, such 
as the Hardmuth soft gray cleaning rubber. To 
erase ink from tracing cloth an eraser of fine spun 
glass held in a pencil-shaped holder is one of the 
latest and best. 

Drawing Board. — T Square. — Triangles. — The 
drawing board should be made of a soft wood, well- 
seasoned white pine or yellow poplar preferred, 
so that the thumb tacks may be easily pushed into 
or drawn from it. The left-hand edge of the board 
must be perfectly straight, as well as smooth and 
free from high spots. 

A T square of well-seasoned pear wood with a 
thirty inch blade is inexpensive and should give 



8 PRINXIPLES OF ENGINEERING DRAWING 

satisfactory results. The inside edge of the head and 
the upper edge of the blade, which are set at right 
angles to each other, should be perfectly straight 
and smoothly and accurately finished. 

Triangles of some transparent material, such as 
celluloid, are preferable, as they are easily kept clean 
and are convenient to use on account of their trans- 
parency. An eight-inch 45° and an eleven-inch 30°- 
60° triangle will be found satisfactory for general use. 

When using these tools, the head of the square 
is held against the left-hand edge of the board and 
the upper edge of the blade used as a ruhng edge for 
all horizontal lines. For vertical hues, hold square 
as mentioned above, also hold one of the triangles 
as shown in the illustration, Fig. 4, and use the 
left-hand edge of the triangle for a ruling edge, al- 
ways drawing the pencil away from the square blade 
when ruling a vertical line. To rule Hues properly, 
lean the top of the pencil slightly away from the 
ruling edge so that the pencil point will slide along 
in the corner formed by the ruling edge and the sur- 
face of the paper. 

Scale. — A flat 12-inch scale graduated in sixteenths 
on the full-size edge and in thirty-seconds on the quarter- 
size edge is most suitable for our purpose, as the 
fractions most commonly used on mechanical drawings 
are multiples of those numbers. A scale with white 
edges and dark graduation lines is highly desirable, 
as the use of this type is least trying on the eyes. 

The student should become familiar with the use 
of this scale in marking off measurements, as this 
part of the work is of much importance in making 
accurate drawings. 



DRAWING TOOLS AND METHODS OF HANDLING 9 

The simplest plan to follow in laying off a given 
length is, to first rule a light, thin line (generally 
termed a construction line) in the proper position, 
then place the edge of the scale just against the line, 
now mark small pencil points on the line, directly 
opposite the graduations on the scale which indicate 
the desired length. Now using the square or tri- 




FiG. 4 



angle as a ruling edge, make the line heavy between 
the two points and the result is the finished line of 
the proper length. 

Dtawing to Measurements. — For practice in the 
use of the tools we have described, it is suggested 
that the student lay out the following figures with 
care in an effort to obtain accurate results: 

Lay out an 8-inch square in the following manner: 



10 PRINCIPLES OF ENGINEERING DRAWING 

First draw in the sides with Hght, thin Knes, then 
when the proper sizes are measured off run over 
the hues again, making the outHne of the square 
heavy. Also lay out a 4-inch and a 2-inch square 
on the same sheet of paper. 

Draw a hght line diagonally across each square; 
that is, a line from far corner to far corner, or the 
longest straight hne that can be drawn inside of each 
square. On this diagonal hne, lay off points or 
measurements as follows: For the 8-inch square these 




Fig. 5 

points should be \ inch apart, starting at one corner 
and letting the last measurement come what it will, 
on the 4-inch square make the points ^ inch apart 
and on the 2-inch square \ inch between points. 
Now using the T square and 45° triangle, with the 
triangle as the ruhng edge, draw hght hues through 
these points in each square, these lines to be at 
right angles to the diagonal line. 

When drawing in these lines, care must be taken to 
see that they cut the center of the point and the 



DRAWING TOOLS AND METHODS OF HANDLING 11 

finished result should be three figures similar to that 
shown in Fig. 5. 

Drawing Instruments. — The illustration, Fig. 6, 
shows a set of drawing instruments which includes 




Fig. 6 



all of the pieces necessary for the general run of 
work in a commercial drafting room. This set 
includes a large compass with pen and pencil points, 
lengthening bar, large adjustable divider, large and 






Fig. 



small ruUng pen, spring bow divider, pencil and 
pen, screw driver and tube for leads. 

In adjusting the instruments for use, place just a 
touch of vasehne on each of the screws and see that 



12 PRINCIPLES OF ENGINEERING DRAWING 

it is spread along the threads as this will keep them 
from wearing rapidly or stripping. When preparing 
the compass points, set the needle with the shoulder 
end out about J inch from the end of the compass. 
Adjust the lead about even with the needle point; 
now with the file produce a flat point somewhat like 




Fig. 8 

a chisel point (except that it is dressed off on both 
sides); this flat pencil point should be set at right 
angles to the needle point and about even with the 
shoulder of the latter. After setting the lead properly, 
file off the corners of the flat point as shown in Fig. 7, 
and the result should be a fairh^ narrow flat pencil 
point, which is slightly shorter than the needle point. 



DRAWING TOOLS AND METHODS OF HANDLING 13 

Handling Compasses. — It is of importance to form 
the habit of handling tools in a workmanlike manner. 
When setting the large compass to a dimension on 
the scale, do this in an easy, natural manner as il- 
lustrated in Fig. S, holding the scale with the left 
hand and using the thumb to help locate the needle 
point. The compass is held in the right hand, the 
adjustment of the legs being controlled by the thumb 
and the first three fingers. 

Where the radius desired is large, bend the compass 
legs at the middle joint so as to keep the legs fairly 
perpendicular. Figure 9 illustrates this point and 
also shows the method of holding the compass 
when throwing in a circle. 

When setting the spring bow^ compass, use the 
method shown in Fig. 10, as by this means the 
scale and compass points are both easily seen, which 
is an important feature; and further with this posi- 
tion, by rolling the adjusting nut between the thumb 
and second finger it is very easy to obtain the desired 
measurement accurately. 

Finding Radius Center. — Before starting some 
of the problems which follow it, may be well to ex- 
plain an excellent method of finding the radius 
center when throwing in round corners. The method 
suggested, for lack of a better name, we have given 
the title ^' trial method,'' as it is by trial that we 
locate the proper position for the compass needle. 
This method applies equally well to all angle corners, 
and tends to promote speed in production. 

To find the radius center, place the compass in 
such a position that the lead point rests directly 
upon one of the corner lines which are to be joined, 



14 PRINCIPLES OF ENGINEERING DRAWING 




Fig. 9 




Fig. 10 



DRAWING TOOLS AND METHODS OF HANDLING 15 



then rest the needle point lightly on the paper in the 
position which the eye indicates as the center. Now 
balance the compass lightly on the needle point and 
swing the lead point around to the other corner 
line; if this point comes directly on the line, the 
needle position is correct and the radius may be 
thrown in. If this position is not quite right, swing 
the lead point back to the original line, balance on 
this and shift the needle point the amount judged 
to be necessary. 

Practice Problems. — The following problems have 




/ 



been prepared for the purpose of furnishing practice 
in the use of the instruments. Using hght, thin 
construction lines, lay out a 4-inch square, an equi- 
lateral triangle with 5-inch sides, and a rhombus 
with 5-inch sides. The smaller angle between the 
sides of the latter figure is to be 45°. Round the 
corners of each of these figures with a J-inch radius, 
using the trial method to find the radius centers. 
Make these round corner lines fairly heavy when 
throwing them in, then ^^ line in " the rest of the 
figure, making the whole outline of the same thickness 
as illustrated for the square in Fig. 11. 



16 PRINCIPLES OF ENGINEERING DRAWING 





1— « 

6 



DRAWING TOOLS AND METHODS OF HANDLING 17 




Fig. 13 




Fig. 14 



Lay out three l|-inch circles tangent to one an- 
other (so that each circle touches the other two). 
Surround these circles by a tangent equilateral tri- 



18 PRINCIPLES OF ENGINEERING DRAWING 

angle. ^^ Line in '' the triangle and test it for ac- 
curac}^, using the large divider; the sides should be of 
equal length. Repeat this several times. 

Lay out a full-size pencil drawing of the hexagon 
and square nuts shown in Fig. 12. In this problem 
the student will encounter three new features; one, 
the use of lines formed of short dashes, which are 
used to indicate a hidden surface; in this case, the 
untapped hole in the nuts. The other features are, 
the use of the circle to construct a figure, and the 
practice of laying out one view (in this case the top 
view) and from it projecting certain surfaces of the 
other views. 

When laying out the top view of the hexagon nut, 
we first throw in the circle representing the diameter 
across flats (3 J inches), then with the T square and 
the 30°-60° triangle construct the outline. We 
follow the same plan for the square nut except that 
we use the 45° triangle with the T square in con- 
structing the outhne. 

]\Iake full-size pencil drawing of the stuffing-box 
gland shown in Fig. 13. 

Make a full-size pencil drawing of the link arm 
shown in Fig. 14. 



CHAPTER III 
LETTERING AND FIGURES 

Lettering. — When selecting a lettering system 
certain fundamentals should be kept in mind, such 
as simplicity and legibility. In other words, a type 
should be chosen that is simple and easy to construct 
freehand and which may be read easily and quickly, 
due to a certain individuality of the letters. 

Many commercial drafting rooms, probably a 
majority, use the w^ell-known Reinhardt system of 
lettering or some modification of it. Modern drafts- 
men are under obligation to Mr. Charles W. Rein- 
hardt, the author of this system which has so largely 
displaced the mechanical abominations of twenty- 
five or thirty years ago. 

When the student fully appreciates the fact that 
much of the information given on a mechanical 
drawing is furnished by means of printed notes, 
headings, titles, etc., he will come to a better realiza- 
tion of the importance of lettering in its application 
to this type of drawing. 

The standards of the better drafting rooms are 
such that only lettering of excellent quality is ac- 
cepted, for these firms take a legitimate pride in the 
fact that drawings bearing their name should convey 
an impression of high-class workmanship, which is 
in keeping with their manufactured products. 



20 PRINCIPLES OF ENGINEERING DRAWING 

Figure 15 illustrates a simple anal3^sis of the Rein- 
hardt freehand system which is used throughout this 
text. A careful stud}^ of this illustration will show 
the order and direction of the various strokes used 
in forming these letters. The student should also 
study the proportions of the letters, especially noting 



Slope of Letters a net Figures 




Fig. 15 

those of the Lower Case, which are proportioned to 
take four spaces, two for the body of the letter and 
one space each above and below the body. 

The use of guide lines, both horizontal and slope, 
as an aid in learning correct lettering should be 
encouraged, as these lines are very helpful and are 



LETTERING AND FIGURES 21 

in fact a necessity for the beginner. These letters 
have a slope of from 1 to 2J as indicated by the little 
figure used as a guide for the slope lines. All of 
these guide lines should be light lines, distinct enough 
to be seen readily but to be decidedly secondary to 
the Unes of the letters. 

Figure 16 illustrates a little lettering triangle 
which most students can make for themselves out 
of a piece of an old T-square blade. This useful 
tool is proportioned to give the slope of from 1 to 2J 
so that it may be used to rule in slope guide Unes. 



Slope / fo 2i 




Fig. 16 



The notches or steps at the tip are useful for 
ruling in the horizontal guide Unes in the following 
manner: Place the triangle against the edge of the 
square blade (slope side up) with the pencil point 
against one of the steps, now slide pencil and triangle 
along the square blade and as the step holds the pencil 
away from the blade, the thickness of the step, the 
upper of two guides lines is produced, the lower 
guide line being ruled from the square blade. This 
device saves the time which would be required by using 
a scale to lay out the positions of the guide lines. 



22 PRINCIPLES OF ENGINEERING DRAWING 

The thickness of the three steps represents the 
three heights used for the lettering in this text, -^ 
inch for the body of the Lower Case letters, with | 
and -^ inch for the Capitals. 

Care should be used in selecting a pencil for free- 
hand lettering; H, or 2H at most, should be used. 
If the pencil is too soft it will smear and the point 
will not last long; if too hard it will cut into the 

Examples ; 

Note on Drai/y/n^_ Make pattern to dasti lines 

tieaG/ing BiL L OF Ma TERIA L 

Title WESTINGH0U3E ELECTRIC Kc MFG. CO. 

PITTSBURGH, PA.^U.S.A. 

200 KW. DC. COUPLED GEN. 

t2S V. 6 P ^7S R.P.M. 

AR/VIATURE ASSEMBLY 

SCALE ^ 5/zf D^G.No. B 136254- 

Fig. 17 

paper and if just right the point slips over the paper 
as if greased. 

The capital letters are used mainly for all titles 
and headings, while the lower case are used for all 
notes on drawings. Figure 17 gives certain examples 
which illustrate their use in practice. 

Figures. — What has been written in regard to 
lettering applies equally well to figures. It is of 
great importance that the student should learn to 
make his figures so well that no one should have any 
trouble to read them easily and quickly. Mistakes 



LETTERING AND FIGURES 23 

in construction are frequently caused by poorly 
written figures on drawings^ and these mistakes are 
often very costly. The value of using great care 
at all times in placing the dimensions on drawings 
is thus clearly shown. 

Problem. — Take a sheet of 11x15 inch draw- 
ing paper and divide the length into three parts of 7, 
5 and 3 inches. Leave a space 1 inch wide across 
the bottom for a title strip. Head the 7 x 10 
inch rectangle on the left, Capitals, the center 
one, Lowxr Case, and the one on the right. Figures. 

Now rule in horizontal guide lines spaced as follows: 
Capitals, | and -f^ inch, half of each; Lower Case, 
^ inch for the body and -^^ inch above and below 
the body; Figures, | inch for the whole numbers 
and I inch for fractions, show several rows of whole 
numbers, some of fractions and some mixed whole 
numbers and fractions. Now rule in slope guide 
hues over the whole sheet. 

When practicing these letters and figures follow 
the strokes in the order illustrated in Fig. 15. Use 
care when printing the fractions, that the parting 
line shall touch neither figure; both should stand out 
clear and distinct. 



CHAPTER IV 
ELEMENTARY PERSPECTIVE 

Perspective. — An elementary knowledge of per- 
spective drawing will be of value to all students as 
a preparation for the study of Orthographic Pro- 
jection. It will also be found useful as a stimulant 
for the reasoning faculties, as the problems given 
cannot be drawn correctly unless a reasonable 
amount of thought a;nd study is devoted to them. 
A little knowledge of this subject will also be help- 
ful in sketching pictorial representations of objects. 

When a picture of a natural object is drawn on a 
plane surface in such manner as to represent that 
object as it would appear to the eye (when seen 
from a single view-point), it is said to be drawn in 
perspective. 

In theory there is a transparent plane (usually 
vertical) between the eye and the object. The cone 
of rays from the eye to the object intersects this plane, 
and if these points of intersection are connected, 
the result is a smaller outhne upon the picture plane, 
which is a duplicate of the view seen from the 
station point of the eye. 

When this object is shown with its vertical sur- 
faces forming an angle with the vertical plane which 
lies between the eye and the object, it is termed 
angular perspective. If the object is a rectangular 
figure and these vertical surfaces form equal angles 



ELEMENTARY PERSPECTIVE 



25 



with the plane as illustrated by the top view of the 
block shown in Fig. 18, it is termed 45° perspective, 
from the fact that this is the angle formed by each 
front surface with the plane. 

In so far as the subject of perspective drawing is 
dealt with in this book it should be understood that 
we are referring to 45° perspective only, as it is not 




Fig. 18 

essential to our purpose to go into this subject more 
extensively at this time. 

Certain well-known phenomena of perspective 
which should be noted and kept in mind by the 
student, when making perspective drawings, are as 
follows: The horizontal lines of an object converge 
toward points on the horizon, whidi are termed the 



26 PRINCIPLES OF ENGINEERING DRAWING 

vanishing points. The horizon, or horizon line, is a 
neutral line on a level with the observer's eye, or 
the station point. Horizontal lines in the object 
above the horizon appear to incline downward 
toward it, while those horizontal lines below the 
horizon appear to incline upward toward it. Hori- 
zontal lines which are parallel converge to the same 
vanishing point. Vertical lines in the object remain 
vertical in the perspective drawing. The dimensions 




Fig. 19 

of an object diminish wdth the increase in the distance 
away from the observer. 

Most of the phenomena just mentioned may be 
observed in the illustration of the building in Fig. 19, 
which photographic view was taken from a point 
on an axis with the near corner, from a height on 
a level with the horizon line. 

While the vanishing points in most of the problems 
given are determined, having been assumed, it is, 



ELEMENTARY PERSPECTIVE 27 

well for the student to be familiar with a method of 
locating these points correctly for angular perspective, 
which is frequently called '' two-point perspective " 
from the fact that all horizontal lines converge to 
two vanishing points. 

At A, in Fig. 18, is show^n a top view of an object 
with one corner touching the line or trace which 
represents the vertical picture plane. The edges 
ab and be form equal angles with the picture plane. 
At S is located the station point of the observer's 
eye; the distance that S is placed from the picture 
plane is a matter of judgment; if too near, the pro- 
portions of the picture are not pleasing, and if placed 
too far away, the picture may be too small or the 
vanishing points may be entirely off of the drawing 
board. 

Having assumed the station point, draw lines 
from S parallel to ab and be through the picture plane; 
the vanishing points are located to the right and left, 
at distances thus found, from the axis Sb which is 
perpendicular to the picture plane. 

At B, in Fig. 18, is shown the view of the object 
seen through the picture plane from the station 
point S. This illustration also shows one method 
of finding the correct length of the horizontal lines 
of the figure. 

Another method of finding the proportions of 
figures is shown in Fig. 20, and as this is the method 
which we shall use it is important that it should be 
studied carefully. This ^^perspective scale" has as its 
basis a one-inch eube, which is to be used as the basis 
when drawing the problems pertaining to this subject. 



28 PRINCIPLES OF ENGINEERING DRAWING 




Fig 20 



In so far as we treat per- 
spective, the 'Vertical measure 
line " is the only line on a 
perspective drawing upon 
which we may lay off actual 
dimensions. If the student 
will think of a point as an end 
view of a line, and will refer 
to A of Fig. 18, he a\ ill under- 
stand why measurements may 
be made on the vertical meas- 
ure line only. Point h in this 
illustration is an end view of 
the vertical measure line, and 
when we represent all surfaces 
back of this point we must 
foreshorten these lines to give 
the true perspective effect. 

When determining the pro- 
portions of the basic cube, 
Fig. 20, point a being assumed 
at a definite position below the 
horizon, lay off dimension ah 
equal to one inch upon the 
vertical measure line, from 
points a and h draw light con- 
struction lines converging on 
the vanishing points, now hy 
eye locate line cd which forms 
the fourth side of one of the 
square surfaces of the cube. 
Do this by using trial Hues, 



ELEMENTARY PERSPECTIVE 



29 



until the impression upon the eye is satisfactory. Line 
ef is formed in the same manner as cd. 

If we assume that Hne ac equals one inch in per- 
spective, half of this line, divided by eye, equals one- 
half inch; this half inch may be divided into quarter 
inch spaces in the same manner, and so on to as small 
dimensions as may be desired. 

The circle in perspective is an ellipse, and the 
illustration, Fig. 21, shows at A the use made of 
the square as an aid in its construction. This 
method has the merit of simplicity and is applicable 





A 



Fig. 21 



to a variety of figures wherein the circle or semi-circles 
are used. 

In addition to the four tangent points at the sides 
of the square, four more points may be located 
on the diagonals by means of the method indicated 
at B, Fig. 21. 

When throwing in a radius to form these circles in 
perspective the compass may be adjusted until the 
radius is suitable to strike three of the eight points 
mentioned, preferably one of the small radii which 
cuts a diagonal point and two sides of the square, 
thus forming the small ends of the ellipse first. 



30 PRINCIPLES OF ENGINEERING DRAWING 










The student should note that the major and minor 
axes of the ellipse do not coincide with the diagonals 
of the square. 

In taking up the problems which follow it is de- 
sired that these perspective drawings shall be made 
on a cross- section pad, as all of the problems have been 



ELEMENTARY PERSPECTIVE 31 

planned with this aim in view. It is further desired 
that one vanishing point only be shown, the Unes 
which would converge on the missing vanishing 
point being located in their proper positions by the 
method indicated in the illustration, Fig. 22. 

Figure 22 illustrates the various stages of con- 
struction when laying out a cube in perspective. 
Having located line ab and drawn in the converging 
lines from a and b to the vanishing point, choose a 
point along the line to the right from a, as at 1, 
where the converging line happens to pass the inter- 
section of two of the Hnes of the cross-section pad, 
locate the corresponding point at the left by means 
of the cross-section lines as at 3, draw a line from 
a through point 3, and we have two lines leaving 
point a which form equal angles with the horizontal 
line through a. Points 2 and 4 wdth converging 
lines are located as above described but it should be 
noted that the angle formed by 62 with the horizontal 
line through b is greater than that formed by al 
with the horizontal line through a, due to the fact 
that b is located lower than a from the horizon. 

The other features of the illustration. Fig. 22, 
should be readily understood from the explanations 
previously given. 

Problems. — In laying out the following problems 
the student is not restricted in the use of tools but 
may use any portions of his equipment desired. 
Care must be taken to complete these drawings 
neatly and accurately. 

Lay out a one-inch cube in three different positions 
below the horizon; one inch, one and one-half inch. 



32 PRINCIPLES OF ENGINEERING DRAWING 

and two inches, from the horizon to the top corner 
marked a in Fig. 22. In each case the vanishing 
point shown is assumed to be eight inches to the 
right of the vertical measure Hne. Place all three 
cubes upon the same sheet of cross-section paper. 




Fig. 23 

Assuming a position two inches below^ the horizon, 
and using one vanishing point located eight inches 
to the right of the vertical measure line, lay out in 
perspective the objects shown in Fig. 23. Take each 
object in the order of simplicity, placing but one 
figure on a sheet of cross-section paper. 



CHAPTER V 

ORTHOGRAPHIC PROJECTION 

Orthographic Projection. — In the presentation of 
perspective drawing we directed the student's at- 
tention to such basic features of the subject as the 
relative positions of the object, the picture plane 
and the eye. Attention was also called to the cone 
of rays, from the eye to the object, which intersected 
the plane. Before taking up the study of ortho- 
graphic projection we again refer the student to those 
features of perspective drawing as we wish them 
kept clearly in mind, so that hy co7nparison we may 
convey a clear understanding of the fundamentals 
of orthographic projection. 

By referring to the illustration of perspective 
drawing in Fig. 24, it will be noted that there is but 
one plane used, and that the rays, or projectors, from 
the eye may form any angle with the plane. Further 
it should be noted that in this perspective drawing 
w^e have one view showing three surfaces of the object. 

Under the rules of orthographic projection we may 
use as many planes as desired, one for each surface 
we wish to portray, but there is this basic difference 
between the position of the picture plane in per- 
spective and that in orthographic projection. In 
perspective the plane may be placed in any position 
we choose, and may forrn any angle with the object, 



34 PRINCIPLES OF ENGINEERING DRAWING 

but in orthographic projection (while the plane is 
between the eye and the object as in perspective) 
the plane must be located parallel to and adjoin the 
surface to be shown. 

There is another basic difference betw^een the two 
methods, perspective and orthographic, to which we 




Plane 



wish special attention paid, and this is the angle with 
the plane formed by the projection lines or rays. 
As previously stated these lines in perspective may 
form any angle with the plane, while in orthographic 
projection they must always be at right angles with 
the plane. 



ORTHOGRAPHIC PROJECTION 



35 



To restate these fundamentals briefly, when mak- 
ing orthographic projection drawings, the plane is 
placed parallel to and adjoining the surface to be 
projected, the projection Hues perpendicular to the 





Fig. 25 

plane are projected out from the object to the plane, 
and the number of planes used depends upon the 
number of surfaces which it is necessary to show to 
convey a clear understanding of the shape and the 
size of the object. 



36 PRINCIPLES OF ENGINEERING DRAWING 

As an aid in presenting the theory of orthographic 
projection the illustration Fig. 25, at E, represents 
three planes placed parallel to three surfaces of an 
object. Upon plane A is projected the top view, 
upon plane B the side view and upon plane C the 
end view of the object. These planes placed in this 
manner lie in positions which are at right angles with 
each other, consequently from a view-point which 
is perpendicular to one of the planes, we cannot 
see the views upon the adjoining planes; it thus 
becomes necessary to revolve these two planes so 
that all three views may be studied from the same 
position at the same time. 

For convenience we may assume that plane B 
is hinged to plane A along line 1-3 and that plane 
C is hinged to plane A on line 1-2. Now we may 
revolve planes B and C up into the same plane as 
plane A in the manner indicated at F in Fig. 25; 
by this means all the views of the object may be 
observed and studied at the same time. 

Figure 25 illustrates the theory of orthographic 
projection which is, or should be, in the mind of a 
draftsman w^hen he makes a three-view mechanical 
drawing of this object. In practice the planes are 
not shown, though for certain t3^pes of drawing 
we frequently show a line or trace to represent the 
planes; in general one view is laid out first (usualh^ 
the view which can be utilized to the best advantage 
to help lay out the other views), and from this view 
are thrown out projection lines as aids in constructing 
the other views as shown in Fig. 26. 

From the foregoing the student should realize that 



ORTHOGRAPHIC PROJECTION 



37 



in laying out mechanical drawings in accordance 
with the rules of orthographic projection, the relation 
between the views is fixed definitely, that while the 
arrangement of the views on the drawing paper is 




a matter of taste, the 
relative positions of 
the views to each 
other may not be 
changed. To make 
this more clear, Fig. 27 
shows three different 

Fig. 26 

arrangements of the views of an object, but the relative 
positions of the views to each other are not changed 
at all. 

Auxiliary Planes. — In the majority of cases the 
projection planes are parallel with vertical or hori- 




iMG. 27 

zontal surfaces of the object to be drawn, but 
it frequently happens that there are certain surfaces 
on the object w^hich do not lie paralM with either 
of these planes consequently a surface of this char- 



38 



PRINCIPLES OF ENGINEERING DRAWING 



acter would be represented by a foreshortened view 
if shown on either a vertical or horizontal plane. 

When an occasion of this kind arises it is neces- 
sary to use an auxiliary plane placed parallel to the 
surface, so that we may project this view in its 




Fig. 28 

true dimensions as indicated by the illustration in 
Fig. 28. 

Reading Drawings. — The ability to read an ortho- 
graphic projection drawing presupposes a training 
which enables one to gain a clear understanding of 
the shape and the size of an object. This under- 
standing is gained only after studying the various 
views of this object shown on the drawing. To 
acquire this ability it is necessary to stimulate the 
imagination as an aid in developing the faculty for 



ORTHOGRAPHIC PROJECTION 39 

mental picturing, for without this power we may 
never be able to read drawings intelligently. 

When forming mental images of objects our nat- 
ural tendency is to think of these mental images in 
perspective form; this is due to life-long habits 
formed from always viewing objects in this fashion. 
One of the reasons for presenting certain problems 
in perspective form is due to a desire to take ad- 
vantage of this tendency. Another reason is that 
when a student is forced to translate perspective 
drawings into orthographic drawings he is obliged 
to use his reasoning faculties, as there is no chance 
to copy and it is only through the exercise of a fair 
knowledge of the fundamentals involved that the 
problems may be solved. 

The problems referred to mil be taken up in the 
next chapter under the head of freehand drawing. 



CHAPTER VI 

FREEHAND SKETCHING 

Sketching. — When an engineer is planning some 
form of construction^ he must have the ability to put 
his ideas on paper in the form of freehand sketches. 
These sketches may be orthographic drawings made 
freehand^ which represent certain views of his crea- 
tion, or they may be pictorial representations. In 
either case he must possess the power to transmit 
to paper the mental image of his creation. 

A new design does not spring fully developed from 
the engineer's brain but is the result of much thought 
and careful study; consequently these freehand draw- 
ings are a distinct aid in the development of the 
design, as they are something tangible which may 
be shaped and changed to suit the will of the designer. 

When attempting to convey an idea regarding 
some mechanism or some form of construction, the 
freehand sketch is one of the commonest methods 
of presenting such matter to those engaged in en- 
gineering work. Sketches made in the shops form 
the basis for many of the working drawings and 
much of the repair work in manufacturing plants. 

Method. — To make sketches which clearly rep- 
resent our ideas it is essential that there shall be 
excellent coordination between the eye and the 
hand, so that these servants of the mind may be made 
to perform our will. It is also of importance to 



FREEHAND SKETCHING 41 

choose a method of making sketches which is simple 
and readily acquired. 

The method we shall follow is called the 
^^Short-stroke Method/' from the fact that as 
we draw a line in any direction, it is not made by 
a single stroke of the pencil, but by a series of short 
strokes. The object of using these short strokes is 
to enable the student to correct an error in direction 
at any point along the line. The result is that the 
general direction of the line is straight^ and though 
there may be slight errors along the hne, they 
cause no doubt as to its meaning. 

The following suggestions will be found helpful if 
studied and carefully followed: As mentioned in 
Chapter No. 2, a pencil of H or 2H hardness sharp- 
ened to a round point (not too sharp) will be found 
generally satisfactory. Learn to hold the pencil 
easily and naturally between the first and second 
fingers and the thumb, never hold it in a stiff or 
cramped manner. 

Do not turn the paper to suit the direction in 
which a line is to be drawn, but fasten it down to 
the drawing board and try to develop that freedom 
of movement of fingers, wrist and arm which will 
enable one to draw with ease a line in any direction. 

The student should sit upright when drawing so 
that he may get a clear view of his work as a 
whole. By having the head well up over the 
work, the eyes can direct the movements of the 
pencil better, as they are in a better position to see 
if the desired shape is growing under the pencil, 
than if held close to the work. 



42 PRINCIPLES OF ENGINEERING DRAWING 



In drawing straight lines, as illustrated in Fig. 29, 
the student should note that Unes drawn in certain 
directions are made by a wrist movement, while in 
other directions a finger movement only is used. 



Wris t movement I in es 
'S> ► 




rmgcn movennenf Unes 




Circle Construction 



r 



\ 



V 



■\ 



; 



Fig. 29 

Construction lines and points are of considerable 
aid in drawing circles, as indicated by the three 
stages of drawing a circle shown in Fig. 29. Par- 
tially laying out a sketch in light construction lines 
and then lining in is also helpful. 



FREEHAND SKETCHING 43 

Proportions. — It is a valuable acquirement, when 
sketching, to be able to make the details of a draw- 
ing of the proper proportions in relation to each 
other. The scale of the sketch is of little import- 
ance, provided it is large enough to show clearly the 
piece or pieces we desire to illustrate, but it is of 
importance that the various parts of an object, or 
the different views of a drawing, shall be drawn to 
the same scale. To obtain this result it is quite 
necessary that the student should train his faculty 
of perception so as to have a well-developed sense 
of measurement, this sense not being confined to 
Hnear measures only but should include angular 
measurements as well. 

The usual procedure when making a sketch of 
an object is, first, to determine what views are 
necessary, then to draw these views completely; 
next, to decide on the dimension lines to suit these 
needs, and, finally, to obtain these dimensions and 
place them on the views of the sketch. 

Problems. — The problems which follow should be 
drawn freehand on cross-section pad; neat, clear 
sketches are desired, using the ^' short stroke " method 
of making lines. Place all dimensions given upon 
the orthographic projection sketches, but leave off 
the dimensions from those problems which are to 
be drawn in perspective. 

Make two-view orthographic sketches of the fol- 
lowing: A 2-inch cylinder 4 inches long, a prism 2 J 
inches square and 4 inches long, a hexagonal prism 
If inches across flats and 4 inches long, a triangular 
prism with 2-inch sides and 4 inches long, a hex- 



44 PRINCIPLES OF ENGINEERING DRAWING 



agonal pyramid 2 inches across flats at the base and 
3 inches in height. 

Make a neat perspective sketch of each of the 
objects shown in orthographic in Fig. 30. 






1 



'-Km 

_i i_ 




,. n 



1_ 



1-^ t^ 



..^r^^cr:, 



A 






i^h^' 



-_.. 



ii 



r^rTT. 




^f 



'i 



■T±r 



1^& ^^"^ 






Fig. 30 



Make a three-view orthographic sketch of the 
clamp shown in Fig. 31. 

Make a three-view orthographic sketch of the 
shaft support shown in Fig. 32. 

Make a three-view orthographic sketch of the 
tool rest shown in Fig. 33. 

Make a two-view (side and edge) orthographic 



FREEHAND SKETCHING 



45 



sketch of the pulley described below, the edge view to 
show^ hub and arms by means of hidden surface 
hnes: Diameter of pulley 14 inches at crown; taper 







■1^ 
4 



"--I 



Fig. 31 




Fig. 32 

of crown equals J inch per foot; face or width 6 
inches. 

Diameter of hub 3f inches; length of hub 4 



46 PRINCIPLES OF ENGINEERING DRAWING 

inches; bore 1| inches; key way -^^ inch wide by 
-j^ inch high. 

Rim made with rib around inside where joined 
to arms. Rim J inch thick at edge, ^^ inch thick 
through crown and rib; inside of rim straight to arms. 




Fig. 33 

Number of arms 6; arms IJ inches wide by f 
inch thick at rim, and If inches wide by ^ inch 
thick at hub; J-inch fillets (or rounded corners) at 
side of arms at hub, and at side and edge of arms 
at rim; f-inch radius at junction of edge of arms near 
hub. 



CHAPTER VII 

ENGINEERING CURVES 

Engineering Curves. — The curves illustrated in 
this chapter are in very common use in engineering 
work, consequently it is desirable to make a brief 
study of the methods of construction. In present- 
ing these methods of construction it should be ap- 
preciated that there are other methods ^^ just as 




Fig. 34 

good " and that the methods chosen happen merely 
to be popular ones. 

Ellipse. — The ellipse has been seen previously 
in the chapter on Perspective, as it is the circle 
viewed obliquely. Four methods of constructing 
the ellipse are shown, of which Figs. 34 and 35 are 
correct and true mathematically, while Figs. 36 
and 37 are near approximations which are very 



48 PRINCIPLES OF ENGINEERING DRAWING 

convenient and satisfactory methods for use under 
certain conditions. 

Assuming a major, or long, axis of 3| inches and 
a minor, or short, axis of 2 inches for Fig. 34, lay 
off these axes to the lengths given; take a straight- 
edge or scale and on one edge mark off the points 
AB equal to half the minor axis; from A mark 
off point C equal to half the major axis. Place the 
straightedge so that point B comes on the major 




Fig. 35 



axis and point C on the minor axis; now, with the 
pencil, mark a point on the drawing paper at A, 
Shift the straightedge and repeat (keeping B and 
C on the major and minor axes respectively), placing 
a sufficient number of points on the paper to enable 
one to trace a curve through them easily. 

The method illustrated in Fig. 35 is one of the 
simplest; the diameters of the circles shown are 
equal to the lengths of the major and minor axes. 
To locate a point on the ellipse, draw a radial line 



ENGINEERING CURVES 



49 



from the circle center cutting these circles; where 
this radial hne intersects the major circle drop (or 
raise as the case may be) a vertical line, from the 
intersection of the radial hne with the minor circle 
throw out a horizontal line; the intersection of this 
horizontal line with the vertical line from the major 
circle is the desired point on the curve of the elHpse. 
At Fig. 36 is shown the " three-radii " approxi- 
mation which is constructed as follows: Construct 




Ftg. 36 

the rectangle ADCEB. Draw the diagonal AC. 
Through D draw DF at right angles to AC. Then 
F is the center for arc GCH, and J is the center 
for arc KAL. 

Make OM = OC. Describe the semicircle AM. 

Make OP = CN. With center F, describe arc 
RPS. 

Make AQ = ON. Then, with J as center and 
radius JQ, describe arc intersecting arc RPS at 
T. T is the center for the tangent arc LG. 



50 



PRINCIPLES OF ENGINEERING DRAWING 



To construct the elliptical curve shown at Fig. 
37, divide the base lines of the curve into the same 
number of equal parts (any number) and connect 
these division points by straight lines. The com- 







Fig. 37 

bined outer surfaces of these lines form the desired 
curve. 

Cycloid. — The method followed in laying out 
the following curves is based upon the principle of 
generating the path of a moving point. 




Fig. 38 

The cycloid is the curve generated by a point 
which is located on the circumference of a circle 
when this circle is rolled along a straight line. When 
the generating circle is rolled upon another circle, 
an epicycloid will be generated. When the gen- 



ENGINEERING CURVES 



51 



erating circle is rolled inside another circle, a hypo- 
cycloid will be generated. 

To generate the cycloid mechanically, lay off the 
base and the center lines; set the dividers to any 
short space (so that the length of the chord is about 
equal to the arc), in this instance \ inch, and step 
off 16 or 18 points on the base line. Erect per- 

EpicycJoid 




pendiculars through these points; swing in the 
generating circle from these different points, so as 
to place the circle in the various positions which 
it would assume in making one complete revolution. 
Now, with the dividers, step off on the second circle 
the distance it has rolled along the base line, in 
this case \ inch. Repeat for each new position of 



52 PRINCIPLES OF ENGINEERING DRAWING 

the generating circle {stepping with the dividers the 
distance around the circle that it has rolled along 
the base line), until a complete revolution has been 
made, then trace the curve through the points thus 
found. 

The epicycloid and hypocycloid are generated 
in the same manner, the base circle replacing the 
base line. 

Involute. — The involute is the curve generated 

ln\/oluie 




Fig. 40 

by every point on a cord as it is wrapped upon or 
unwound from a cylinder. 

To develop the involute mechanically, unwind a 
little bit of the cord at a time, and step off upon 
the line the distance unwound. Set the dividers 
to \ inch and step off 10 or 12 divisions upon the 
base circle; from these points draw tangent lines 
to represent the cord in different positions when 
being unwound. Then, with the dividers, step off 
on these tangent lines the number of points away 
from zero which each line is placed. Connect the 



ENGINEERING CURVES 



53 



outermost point on each line and we have the desired 
curve. 

Helix. — The heUx, or screw, is the curve which 
would be generated upon a cyUnder revolved at a 
constant speed against a point, the point mean- 
while moving along at a constant speed parallel 
with the axis of the cylinder. 

To generate this curve mechanically, divide the 
circumference of the cylinder into any number of 

Helix or Screw _ 2 Pitch 



Si S5 71 I) I? IS 13 1/ 9 7 S3 I 




Fig. 41 

equal parts, in this case 25, numbering these points 
from the left on the center hne, as shown in Fig. 
41. Divide the pitch distance on the cyhnder into 
the same number of equal spaces (25) by which the 
circumference of the cylinder was divided. Now 
locate points on the side view of the cyhnder, at 
the intersection of the vertical division lines with the 
horizontal projection lines from the points on the 
end view of the c^dinder; then trace the curve 
through the points thus found. 



CHAPTER VIII 

CONIC SECTIONS— INTERSECTIONS AND 
DEVELOPMENTS 

Conic Sections — Intersections. — A little study 
of the subject of conic sections and the intersections 
of surfaces should demonstrate the fact that ortho- 
graphic projection is the basis for the solution of 
such problems as are here presented. Further study 
should bring out the fact that points and lines are 
the basic elements used to obtain this solution, for 
by their use curves and sections of circular figures 
may be projected in very simple fashion. 

In general the subject matter of this chapter may 
be studied from three fairly distinct points of view. 
As subject matter in the study of descriptive geom- 
etry wherein these solids would serve as a basis for 
studying the theory of surfaces, portions of the 
subject matter may be considered simply as prob- 
lems in orthographic projection, and, finally, the whole 
may serve as the basis for practical work in draft- 
ing patterns for sheet metal workers. 

Our desire is to present this matter as a study in 
orthographic projection and the development of 
surfaces, to the end that the student may be better 
prepared to solve the varions difficult drafting prob- 
lems which the engineer is apt to encounter. 



INTERSECTIONS AND DEVELOPMENTS 



55 




-5 



6 

I— I 







56 PRINCIPLES OF ENGINEERING DRAWING 

The illustration in Fig. 42 shows a cone cut by 
a plane in two different ways. When a cone is cut 
by a plane which passes between the apex and 
the base at any angle (except a right angle) the 
section will be an ellipse. If the cone is cut by 
a plane which is parallel with one side, the section 
made is a parabola. 

Problems. — Lay out the cones to the dimensions 
given. Divide the base circle of the top view into 
any number of points equally or unequally spaced; 
from these points draw lines to the apex; now 
project the lines down onto the side view. The 
student will find it a convenience to make the line 
spacing on the upper half of the top view a duplicate 
of that on the lower half. 

To develop the ellipse, cut the cone as shown in 
the side view; the points made by the intersection 
of the cutting plane with the slope lines should then 
be projected to the same lines in the top view. By 
connecting these points we have a true ellipse. 

In developing the parabola, place the cutting 
plane through the side view as indicated, and pro- 
ject the points of intersection to the top view in the 
same manner as for the ellipse. With the top and 
side views complete, it is quite a simple matter to 
develop the front view, point by point, as shown in 
the illustration. 

Intersection of Cylinders. — The illustration. Fig. 
43, shows two intersecting hollow cylinders and the 
developments of their surfaces. 

To construct the curve of intersection of the two 
cylinders, divide the end view of the small cylinder 



INTERSECTIONS AND DEVELOPMENTS 



57 




58 PRINCIPLES OF ENGINEERING DRAWING 

into any number of points (for convenience an even 
number in this case), then project these points onto 
the other views. The curve is found point by 
point as indicated by points 2 and 4 on the ihustra- 
tion. The elHpse shown on the end plane is formed 
b}^ cutting the large cylinder off at an angle of 30° 
with the horizontal plane; it is constructed in the 
same manner as the curve of intersection. 

Development of Surfaces. — In most forms of 
sheet metal construction it is customary to prepare 
a pattern or templet on a flat surface, this pattern 
being of such outline that when it is formed or 
folded into its final shape it will form a part, or, 
in some simple patterns, the whole of the object 
for which the pattern was developed. 

In commercial plants the drafting of these pat- 
terns is done with a high degree of accuracy, with 
the proper allowance for seams, and where the sheet 
stock is thick, as for boilers and tanks, allowance 
must also be made for thickness of plate, riveted 
joints, etc. 

The different methods of developing a surface 
are usually described by the types of lines used for 
this purpose. As an instance, in our present problem 
we use parallel lines to develop the surfaces of the 
cylinders, hence the term " Parallel Line Develop- 
ment." 

To construct the cylinder development, project 
the division points from the end view to the side 
view parallel with the cylinder axis. Find the cir- 
cumference of the cylinder (by calculation, not by 
stepping it off with the dividers), lay off a base line 



INTERSECTIONS AND DEVELOPMENTS 59 

representing this length, upon which place the 
division points correctly spaced; from these division 
points erect parallel lines or coordinates. The length 
of these lines may be found by projection from the 
side view or these lengths may be transferred with 
a compass. 

Intersection of Cone and Cylinder. — The illus- 
tration, Fig. 44, shows a cylinder intersecting a cone; 
the curve of intersection is found in much the same 
manner as that of the intersecting cylinders, but 
with this vital difference that it is fii^st necessary to 
project the radial lines from the view on the end 
plane to the top view, so as to have an element upon 
which to project the points. 

A simple method of construction is to draw in 
these radial lines from the apex to the base of the 
cone through the end view of the cylinder, let the 
first line be tangent to the cylinder and the other 
lines be located by eye as shown. The points 
formed by the intersection of these radial lines with 
the end of the cylinder may be used to produce the 
curve as indicated by points 1 and 4. 

Radial Line Development. — The second method 
of development is derived from the shape of the figure, 
the surface of the cone necessitating that radial 
lines be used in its development, from which we get 
the term ^' Radial Line Development.'' 

When laying out the development of the cone, 
the student should bear in mind that the true length 
of the lines on the cone can be found on the " slant 
height " or the sides of the cone only, as in all other 
positions the lines are foreshortened. 



60 



PRINCIPLES OF ENGINEERING DRAWING 




INTERSECTIONS AND DEVELOPMENTS 61 

Thus to get the true distance from the apex of 
the cone to point 1, this point must be projected to 
one of the sides. The student should also remember to 
use the same radial lines for the development that 
were used in finding the curve of intersection. 

Triangulation Development. — One of the com- 
monest methods of development derives its name from 
the fact that the surfaces of certain forms of con- 
struction may be divided up into a series of triangles. 

To construct the development of the transition 
piece shown in the illustration, Fig. 45, first lay out 
the top and side views, dividing up the surface into 
triangles and marking the lines with letters and 
figures as shown. Then find the true length of each 
line by the method indicated in the illustration. 
Now, using these lines with the top and base lines, 
construct the triangles into which the figure had 
been previously divided. Connect these triangles 
in the manner indicated by the partial development 
shown in Fig. 45, and the result will be the complete 
pattern desired. 

Problems. — Make developments of the cone sur- 
faces remaining below the cutting planes in Fig. 42. 

Lay out a hexagonal pyramid which is 3 inches in 
diameter across flats at the base and 4| inches high. 
Cut this pyramid 1| inches below apex by a 45° 
plane. Make a development of surface of pyramid 
below plane. 

Make an intersection drawing and the develop- 
ment of two cylinders. The large cylinder is 2j 
inches in diameter by 4 inches long. The small 
cylinder is IJ inches in diameter by 1 inch long on 



62 PRINCIPLES OF ENGINEERING DRAWING 




INTERSECTIONS AND DEVELOPMENTS 63 

short side; axis of small cylinder lifted to an angle 
of 45° intersects circumference of large cylinder 
2 inches above the base. 

This problem is an excellent illustration of the use 
made of auxiliary planes. 



CHAPTER IX 
ISOMETRIC AND OBLIQUE DRAWING 

Isometric Projection. — It is frequently necessary 
for the mechanical draftsman to make one-plane 
projection drawings of certain forms of construction. 
If these illustrations are prepared as they would 
appear from a single view-point they are termed 
perspective drawings. 

Perspective drawings best illustrate this type of 
work from the fact that they represent the object 
as it would appear to the eye; at the same time 
there are certain disadvantages connected with this 
system. The main objection is that these drawings 
cannot be laid out from dimensions as mechanical 
drawings are, and this one disadvantage is quite 
serious from the point of view of the draftsman. 

Isometric, or equal measure projection, is a fairly 
satisfactory substitute for perspective drawing for 
certain classes of work. 

This method may be termed approximate per- 
spective, as it represents an object in such fashion 
that it looks approximately as it w^ould appear to 
the eye. The primary difference between two draw- 
ings of an object, one in perspective and the other 
in isometric, is that in the perspective drawing the 
surface lines converge at a certain distance from the 
object, as shown in Fig. 46, while in the isometric 
drawing these same surface lines are parallel. 



ISOMETRIC AND OBLIQUE DRAWING 



65 



For certain shapes, or at least for some views, 
isometric drawings are not satisfactory, as the figure 
appears badly distorted and unpleasing to the eye, 




Perspective 
Fig. 46 



/somefric 



but for most subjects it will be found quite satis- 
factory. 

Isometric projection is based on the theory that 




P/onc 



izo 




Isometric Axes 



Fig. 47 



the object is viewed through a plane with which 
certain main features of the body are equally fore- 
shortened. To illustrate, the cube shown in Fig. 
47 is tilted forward until the edges AB, AC and 



66 



PRINCIPLES OF ENGINEERING DRAWING 



AD are equally foreshortened as seen through the 
plane. 

This figure also illustrates what are known as the 
isometric axes and their origin, as these three edges 
of the cube (AB, AC and AD) considered as Unes, 




^Cuffing Plane 
Fig. 48 

are separated by an equal angular space and cor- 
respond to the three dimensions, length, breadth 
and height. 

Figure 48 represents a two-view mechanical draw- 
ing of a cube, from which is projected (orthograph- 



ISOMETRIC AND OBLIQUE DRAWING 67 

ically) an isometric view of the cube. This illus- 
tration shows the transformation from mechanical to 
isometric, the relationship between these two methods, 
and makes clear the sound basis from which iso- 
metric projection was derived. 

To demonstrate the theory that the surfaces of 
the body are equally foreshortened, we place the 
cutting plane through points B, C and D of the 
cube; then as the projection plane is located parallel 
with the cutting plane, the portion of the cube cut 
away (as indicated by the dash lines in the isometric 
view) forms a triangular pyramid with corners of 
equal length. 

The student should try to remember the following 
fundamental principles of isometric projection: 

There are three basic lines known as isometric 
axes. 

Isometric axes are separated by an equal angular 
space, and correspond to the dimensions, length, 
breadth and height. 

Vertical lines on the object are vertical lines on 
the drawing. Lines parallel on the object are par- 
allel on the drawing. Right angles on the object 
are either 60° or 120° on the drawing; 

Lines not parallel to one of the isometric axes are 
termed non-isometric lines. Measurements may be 
made only on isometric lines. 

Isometric Drawing. — When a drawing has been 
made according to the rules of isometric projection^ 
the isometric lines forming this drawing are eighty- 
one hundredths (0.81) of their true length. As this 
necessitates using an isometric scale, it is generally 



68 PRINCIPLES OF ENGINEERING DRAWING 



considered good practice to use an ordinary scale 
to lay out the figure to the dimensions given. The 
result will be an isometric drawing, not a projection, 
but as the only difference is in the size of the figure, 
this is of little importance. 

Coordinate Axes. — When laying out isometric 
drawings of certain shapes, a very convenient aid 



C J 


'___J 


S 


i_ 


\ 




D 1 


^ 


=1 





Fig. 49 

is the related axes, usually termed coordinate axes. 
Figure 49 illustrates this feature as it shows how 
the isometric view of a triangular pyramid may be 
constructed with the aid of these axes and the 
mechanical views. 

To construct Fig. 49, lay out the mechanical views 
as shown, then draw a rectangular figure about the 
top view (as indicated by A BCD). This gives a 



ISOMETRIC AND OBLIQUE DRAWING 69 




O I Z 5 4- 3 e 7 a 9 lO II 12 




Fig. 50 



figure that parallels the isometric axes and on which 
we may locate the base of the pyramid. After this 
has been done, find the point of intersection of the 



70 PRINCIPLES OF ENGINEERING DRAWING 

axes (1-2 and 3-4) on this figure, and from this 
point erect a perpendicular on which lay off the 
height of the p^^ramid. Now then connect the apex 
point with the corners on the base and the figure is 
complete. 

To emphasize the convenience of these related 
axes, the student is reminded that measurements 
may be made only on isometric lines, and as the 
lines forming the outline of the pyramid base are not 

4- Center Construction 




Application of 4- Center Mettiod 

Fig. 51 

at right angles with each other, only one side may 
be placed on an isometric axis. 

Figure 50 shows the application of the coordinate 
axes to quite a differently shaped figure from our 
last illustration. The mechanical view of the side 
of the piece is divided into a certain number of parts 
(any number), spaced either evenly or unevenly; 
then these lines or axes are used as shown when 
constructing the isometric view. Two applications 
are shown, one of which is pleasing to the eye and 
the other quite the reverse. 



ISOMETRIC AND OBLIQUE DRAWING 71 

Isometric Circles. — The methods of constructing 
isometric circles should require little explanation 
and their application to rounded corners should be 
readily understood from the illustration, Fig. 51. 

For general purposes the four-center method will 
be found satisfactory and, with a Uttle study of the 



Core 




Fig. 52 



illustration, the student should be able to apply this 
method to his work. 

One feature which it is well for the student to bear 
in mind is that to construct any circle arc, he should 
lay out an isometric square of the circle diameter as 
a means of locating the position of the radius center. 



72 PRINCIPLES OF ENGINEERING DRAWING 

Problems. — ]\Iake an isometric drawing of a 
hexagonal pyramid. Size of pyramid 3 inches in 
diameter across flats at base by 4 J inches high. 



Round opening as shown 




I Sfock 

Fig. 53 




Fig. 54 



Make an isometric drawing from the bracket 
sketch in Fig. 52. 

Make an isometric drawing from the broom holder 
sketch in Fig. 53. 



ISOMETRIC AND OBLIQUE DRAWING 



73 




h-/f 



Fig. 55 




1 '--lOi 



Fig. 56 



74 PRINCIPLES OF EXGINEERING DRAWING 



Make two isometric drawings, one showing the 
back and the other the face, from the lathe face 
plate sketch in Fig. 54. 

Make an isometric drawing from the shelf sketch 
in Fig. 55. Owing to the length of this object it 



Li 



^ 



T 



JL 



V 



^ 



I-/, 




^ 



r 



6 

4 



6 " 



A 



T 







^ Cored holet 



Fig. 57 

will be found necessary to '' break " the shelf or to 
draw it to a scale of less than full size so that we may 
use one of the standard sheets of drawing paper. 

Make an isometric drawing of the corner shelf 
shown in Fig. 56. This drawing to represent the 
axes reversed; that is, the view is taken from helow 



ISOMETRIC AND OBLIQUE DRAWING 75 

and directly in front of the center of the shelf, as if 
the shelf were tilted backward. 

Make an isometric drawing of the bracket shown 
in Fig. 57. This drawing also to represent the 
reverse axes. 

Oblique Drawing. — As isometric projection is an 
approximation of angular perspective, so oblique 
projection may be compared as an approximation 
of parallel or one point perspective. 

The basis of oblique projection is to place one 
surface of an object parallel with the picture plane 
as in orthographic projection, this surface being 
drawn to its true dimensions. Surfaces of this ob- 
ject, which are normally at right angles with the 
front surface, may be shown at any angle with this 
face. The angles which are in most common use 
are 45° and 30°, due, in a large measure, to the 
convenience of having triangles of these angles. 

Figure 58 shows an obhque drawing of a cube, 
the corners A-B, A-C and A-D representing the 
axes. Measurements may be made on lines parallel 
to these axes; circles are constructed as in isomet- 
ric, though the radii centers may fall outside of the 
construction square under certain conditions. In gen- 
eral the method of drawing is quite similar to iso- 
metric, but with this difference, the isometric system 
may be projected direct from orthographic views, 
while the basis of the oblique system is arbitrarily 
assumed. 

Cabinet drawing is similar to oblique drawing with the 
exception that lines parallel to the cross axis A-C, 
in Fig. 58, are made one-half their true length in an 



76 PRINCIPLES OF ENGINEERING DRAWING 



O 




4 



J 



Vr- 



-4 



V, 



y 












'^ 



L'^ 



X-_r 



i 



N^ 






Fig. 59 



ISOMETRIC AND OBLIQUE DRAWING 77 

attempt to approximate the foreshortening effect of 
perspective. 

Problem. — At Fig. 59 is shown a two-view ortho- 
graphic sketch of an object from which the student 
is expected to make an obhque drawing, bearing in 
mind that there is less Hability of a distorted view 
if the irregular face of an object is placed parallel 
with the picture plane. 



CHAPTER X 

DRAFTING ROOM CONVENTIONS 

Drafting Room Conventions. — The engineering 
student should have a fair working knowledge of 
certain customs or practices which are in general use 
in commercial drafting rooms. These conventional 




Hidden line 

Break lim 



Visible Outline 
Section line 

Center line 



Fig. 60 

methods vary with different firms, but it is com- 
paratively easy to learn these variations if one is 
familiar with the customs which are generally known 
to the engineering profession. 

Lines. — There is a reasonable degree of uniformity 
among commercial drafting rooms in regard to the 



DRAFTING ROOM CONVENTIONS 



79 



use of certain types of lines to indicate surfaces and 
to convey certain ideas. With some variations the 
Hues shown in Fig. 60 are in common use for the 
purpose indicated clearly in the illustration. 

Screw Threads. — Figure 61 illustrates a number 
of screw-thread cross sections; this illustration is 
intended to give the student an idea of the propor- 
tions of these different types of threads, each of 
which is well suited for some particular purpose 
in engineering work. 

ScREi^ Threads 

■60' 




U. S.Sfandard 
■ 29' 



r'1 




Sharp 1/ Square 

Taper = ^ per foof on dia. 



Acme 




Ripe 



Fig. 61 

Generally speaking, we do not show true represen- 
tations of screw threads on working drawings, there 
are at least two good reasons for this: one is the 
excessive cost, and the other, that it is unnecessary. 
Instead of taking the time required to draw in 
threads as they really appear, the draftsman uses one 
of the conventional methods to indicate a threaded 
surface. As a rule, the purpose of indicating screw 
threads on mechanical drawings is to inform the 
shop-man where, how far, and what pitch threads 



80 PRINCIPLES OF ENGINEERING DRAWING 



are to be cut on certain portions of an object. Us- 
ually this information is furnished by indicating the 
part to be threaded by one of the conventional meth- 
ods, and by means of dimensions and notes giving the 
specific information necessary. 

Figure 62 illustrates what is possibly one of the 
most simple conventional methods of indicating 
screw threads under different conditions. When in- 
dicating thread by this method it is not essential 



r 



Bolt Length 



Dia. 





Conventional method of 
indicating screw threads 




] f 



-1- 



\ Tap dia. 

Tap Drill dia. 



Fig. 62 

that the space between the Hght lines be just the 
same as the pitch of the thread, or that the Hues be 
sloped at exactly the correct angle, but it is of im- 
portance that the threaded surface as a whole look 
approximately correct; that is, mde spaces for coarse 
pitch and narrow spaces for fine pitch, etc. 

Where the slope is correct for a single-thread 
screw, a Une drawn at right angles to the center hne 
of the screw should touch the end of one of the light 



DRAFTING ROOM CONVENTIONS 



81 



lines at one side and pass midway between that line 
and the next on the opposite side. In other words, 
the slope equals half of the pitch of the thread. 

Fasteners. — When assembling the various forms 
of engineering construction it is necessary to make 
use of a great variety of fastening devices, these 
various fasteners being designed to suit varying 
purposes and needs. Figure 63 illustrates a group 
of fasteners which are in common. use for holding 



Machine Bolts 

Hexagon Square 




Car Screws 

Hexagon Square Oval Fils. Flat Fits. Button F'lat 


















©v^ 






® 







o m a 



n 







Studs 



Machine Sc/?£:>vs 

Oval Fils. Flat Fils. Round Flat 



Fig. 63 

parts together; these devices are used either alone or 
in conjunction with some of the nuts shown in 
Fig. 64. 

These latter also vary to suit the particular pur- 
pose for which they are needed. 

The illustration in Fig. 65 shows a group of fast- 
eners, each of which is in common use as a device 
for locking two revolving parts together so that they 
shall move as one. The fasteners shown are merely 



82 PRINCIPLES OF ENGINEERING DRAWING 

a few of the most common types and each is especially 
adapted for some particular purpose. 

The set screws shown in Fig. 66 are used for a 
purpose quite similar to that for which keys are 

NUTS 




r~s^ — "s^v 



Hexagon 




. 


: 

u 


ll 

ll 
•• 





Square 







Lock 




Wj'ng 

Fig. 64 

Keys 



spanner 



Taper p'ln 



n 



Recfvngular 



Round end 



D C 



3D 



Taper 



Woodruff 



B 




Fig. 65 

needed: that is, to lock two parts together so that 
their relative positions are stationary. These parts 
may be revolving ones, or they may be sliding pieces 
which it is desirable to adjust from time to time. 



DRAFTING ROOM CONVENTIONS 



83 



The headless type of set screw is especially desirable 
for use with revolving parts as there is no project- 
ing head to catch a workman's clothing which may 
come in contact with the revolving mechanism. 

The rivet shown in Fig. 67 is a permanent fast- 
ener, as distinguished from all of the others pre- 
viously illustrated, each of which may be removed 
without undue difficulty unless rusted seriously. 
The balance of the fasteners shown in Fig. 67 are 

Sett ScfPErws 



Square 






Heod/ess 



(ID © 



n 




tr 



v^:=v' 



Round Flat Cone Pin Cup 
Fig. 66 

of the adjustable type used very commonly in bridge 
construction. 

Breaks. — It frequently happens, owing to the 
size and shape of an object, that it is necessary to 
^' break '' out a portion of this object, as illustrated 
in Fig. 68, so that we may be enabled to place it 
on a standard-size sheet of drawing paper. When 
making a '^ break '' of this character, it is necessary 
that the portion taken out shall be of the same size 
and shape as the material left on each side of the 
broken edges, so that no misunderstanding as to the 



84 PRINCIPLES OF ENGINEERING DRAWING 



true size and form of the object may be caused. 
Sectioning. — One of the necessary conventions 
in constant use consists in showing views of objects 
with portions cut away, or ^^ in section/ 'as it is 
generally termed. The main advantage of this con- 
vention is that it enables us to more clearty repre- 

TuRNBucKLC EI^E Bar 





Sleeve Nut 




Clevis 




n 



Rivet 
A 



Fig. 67 

sent the form of a piece and frequently dimensions 
may be placed in a more satisfactory manner on a 
sectional view. 

As an aid in indicating that a piece is in section 
the surfaces touched by the cutting plane are covered 
with hght lines called '' section Unes." These lines 
are drawn with the aid of a 45° triangle as a ruling 



DRAFTING ROOM CONVENTIONS 



85 



edge^ the triangle being held against the T square 
and moved for each hne. Where two or more pieces 
assembled together are shown in section, the different 
parts are shown more clearly by sloping the section 
lines in opposite directions where the parts join. 

In the past it has been the custom to use section 
lines of differing character for different kinds of 
metals. The main purpose of this custom was to 
convey an idea of the material by this means and 

Breaks 

Round Stock 





Rectangular Stock 



l^etal 



Wood 



StrucfuroJ Members 



c 



I 



L 



Fig. 68 



thus to a certain extent prevent mistakes. With 
the use of the '^ Bill of Material '' on the drawings, 
and copies of specifications at hand, there is no need 
to indicate the kind of metal by means of section 
lines as a general custom. 

There is a very decided objection on the part of 
certain large firms to the above-mentioned custom 
and this objection is based upon the ground of 
economy. The form, or finished design, of machines 
is the result of constant change of detail, a process 



86 PRINCIPLES OF ENGINEERING DRAWING 

of evolution based upon experience with various 
materials and with various sizes and shapes. 

When one of these changes of detail is made it 
necessitates changing the old drawings, or making 
new ones, the former usually, if the change can be 
handled satisfactorily in this manner. All such 
changes are an expense but this cost may be reduced 
to a minimum if the change on the drawing is merely 
a change of material, for then the use of the '' Bill 
of Material " permits us to change one symbol for 
another, as C-i to C-S or C-i to B-z, and the 
correction is complete except for the record of the 
change. 

If we use a different type of section line for each 
metal and a sectional view^ is shown of the part to 
be changed, it is necessary to erase the section lines 
of this view on the tracing and replace them with 
the section lines of the new metal. 

This process is so costly to firms with large numbers 
of drawings that it has led to the adoption of one 
style of section lines for all metals with the exception 
of bearing metals, such as Babbitt metal and similar 
alloys. 

To restate this briefly, the use of different kinds 
of section lines to indicate the various metals is 
costly; it is also unnecessary, as we may clearly in- 
dicate materials on the ^' Bill of Material " from 
which specification clerks gain their information. 
Further, we may obtain the effect of contrast be- 
tween parts by varying the spacing and the slope 
of section lines of the type show^n for metal in Fig. 69. 

In this illustration, Fig. 69, no attempt has been 



DRAFTING ROOM CONVENTIONS 



87 



made to show sections of all the materials used in 
engineering construction, but merely those needed 
for metals and some of the more common in use in 
building construction. It should be clearly under- 
stood also that what was mentioned above in refer- 
ence to the use of different types of section lines for 
metals had reference only to manufacturers of some 
form of machinery and not to architectural con- 
struction. 
At Fig. 70 is shown a true section of a flanged 

Sect/ons 







Me fa Is 


Metals 


in 


for 


General 


Bearings 



Wood 



Concrete 







[ZVy^ y-y'^r'^ 



/ / / / / / 



/ .- / / / 



-r—T" / / / 



Brick 



Insulation 



Fig. 69 



pulley, this section being cut along the vertical 
center line of the side view. This section is in 
marked contrast with the illustration in Fig. 71, 
which shows a special section that is common for 
all pieces of this type, such as fly-wheels, pulleys 
and gear wheels with arms. 

This section of the hand wheel is not a true section, 
but a conventional one which is more satisfactory 
for the use of the pattern maker and the draftsman 
as it shows a true cross section of the hub and the 
rim, though not of the wheel as a whole. This 




o 
Z 




o 



30 

30 



DRAFTING ROOM CONVENTIONS 



89 





90 



PRINCIPLES OF ENGINEERING DRAAMNG 



method of sectioning is followed for pieces of this 
type regardless of the number of arms in the wheel. 
Further, the student should note that without the 
small cross section of the arm given in this manner, 
he would be unable to show the shape of this part. 

Figure 72 illustrates the customary method of 
indicating where the sections are taken, by means of 
the hues A-B and C-D. 

The armature spider shown in Fig. 73 is an il- 




Section C-D 



Bore 2.03-4 
' / Top S^-S Thd 

O S.Sfd. 




Fig. 72 

lustration of special sectioning Avhich shows true 
sections cut along the lines indicated. This illus- 
tration has value from at least two other points of 
view, one of which is that it shows a conventional 
method of making a working drawing of a large 
casting on a relatively small sheet of dra^nng paper, 
due to the fact that only a part (one half) of the 
casting is shown. 

This type of working drawing is readily understood 



DRAFTING ROOM CONVENTIONS 



91 




(0 



k3 

o 1^ 



C^ 



92 PRINCIPLES OF ENGINEERING DRAWING 

by the workmen who are accustomed to note that 
many of the dimensions are given in diameters. 
This method of laying out working drawings has 
the decided merit of economy and ma}^ be considered 
as making advanced use of the " break " system. 

Dimensions. — When dimensioning drawings it is 
of fundamental importance to place the dimensions 
in such a manner that they may be readily found 
and easily read. The figures must be printed clearly 




•rmish MarK 




Drill ^e- Tap f 
^Drill^ i'Tap' 

-/of 



2i" 



-? ^ 



~^^~ r— I 

* I ' 



ih 






Fig. 74 



and carefully and so arranged that there is no crowd- 
ing; use plenty of space and plan the arrangement 
so that the various figures are placed in the best 
positions to give the size of the part they represent. 
Figure 74 shows a number of excellent methods 
of placing dimensions so that they may be clearly 
seen. Note should be taken of the '^ finish mark/' 
originated by Prof. George H. Follows, and the il- 
lustration of its use at the ends of the dimension 



DRAFTING ROOM CONVENTIONS 93 

line, which indicates that all surfaces between these 
points are to be finished. The / which is in rather 
common use is contrasted on the adjoining figure. 

Most of the suggestions indicated in Fig. 74 are 
made use of on the working drawing of the armature 
spider, Fig. 73, which is an excellent representation 
of correct methods of placing dimensions. When 
studying this illustration note should be taken of 
the fact that dimensions of twelve inches or greater 
are shown by feet and inches or fractions of an 
inch; but where the dimension is less than twelve 
inches it is indicated in inches. This custom is 
quite common, though some firms begin with twenty- 
four instead of twelve. 

Standard Data. — In commercial drafting rooms 
a constant effort is made to devise ways and means 
to speed up production without, at the same time, 
lowering the standard quality of the product. One 
important means used to gain speed and to improve 
the quality of the product is: to provide uniform 
methods in the drafting room in the production of 
drawings. That is, all of the draftsmen use the same 
symbols, style of lettering, dimensioning and the 
same reference matter, and in all respects are required 
to follow the same standard. 

In a drafting room where each draftsman handles 
his calculations in his own way regardless as to his 
neighbor's method of computing the same sort of a 
problem, and where there is much of this ^^ go as 
you please " lack of method, such a thing as uni- 
formity is out of the question. An infinitely better 
procedure is to determine the best method of handling 



94 PRINCIPLES OF ENGINEERING DRAWING 

these problems which are constantly coming up for 
solution J and to make this method the standard. 

This need of standardization has resulted in many 
firms forming a " Standard Department " within 
the drafting room organization, it being the duty of 
this department to determine which are the best 
methods, and to prepare this information in the 
form of reference sheets to which all draftsmen have 
access. 

Usually these reference sheets, or " Standard Data " 
sheets as they are generally termed, are prepared in 
such form that little or no calculation is necessary 
on the part of the draftsman using them; generally 
speaking he refers to them for certain standard di- 
mensions which are shown in tabular form. 

The subject matter of these data sheets varies from 
the simplest matter to rather complex problems in 
some cases, but their purpose is to save time and to 
aid in producing uniform, accurate drawings. 

Figures 75 and 76 illustrate two simple data 
sheets upon one of which the dimensions are given 
for standard sheets of an excellent size. These 
sheets may be prepared in blue print form and 
bound up in covers for convenience in handling. 

Composite Drawing. — Any satisfactory method of 
representing subject matter in the drafting room 
which reduces the general expense of producing 
drawings is to be commended. By using what are 
knoAvn as " composite drawings," we may save 
making a large number of detail drawings. 

Firms that manufacture a standard line of ma- 
chines usually design them in such a manner that 



DRAFTING ROOM CONVENTIONS 



95 













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96 



PRINCIPLES OF EXGIXEERIXG DRAWING 




8 



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DRAFTING ROOM CONVENTIONS 97 

certain details of these machines are just ahke except 
as to size. This being the case, a drawing may be 
produced which represents all sizes of a particular 
detail. As it would be impracticable to place the 
dimensions of all sizes on this one figure, letters are 
used to designate the various dimensions. Below 
the drawing of the piece a table is laid out with 
these letters as headings, and under each letter the 
dimensions are given for each size of the piece 
illustrated. 

As an illustration of the sa\dng by this method, 
the composite drawing shown in Fig. 77 furnishes 
information for the production of twelve socket 
wrenches of different sizes, this one drawing taking 
the place of twelve, and after one is familiar with 
the method, this t^^pe of drawing is as readily and 
easily used as a separate detail drawing. 

These drawings are of value in the drafting room 
for reference purposes, and they may be prepared 
upon the same size sheets as standard data, and used 
as such. They may be furnished to the shop-men 
who produce the parts, as any notes as to material, 
finish, etc., may be placed upon a drawing of this 
kind as well as upon any other working drawing. 

Abbreviations. — It is a common practice in draft- 
ing rooms to abbreviate words and terms for the 
purpose of saving time and space when printing 
notes on drawings. In furnishing the following list 
of abbreviations our aim is to present some of those 
in quite general use but with no pretension that 
this is a complete list: 



98 PRINCIPLES OF ENGINEERING DRAWING 



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DRAFTING ROOM CONVENTIONS 



99 



A. C Alternating Current 

Br Brass 

Bz Bronze 

C. I Cast Iron 

C. S ■. . Cast Steel 

C. R Cold rolled (Machine 

Steel) 
C. L. or C. . . Center Line 

Csk Countersink 

Cbr Counterbore 

C. P Circular Pitch 

D. and dia. . . Diameter 

D. C Direct Current 

H. P Horse-power 

Hd Head 

Hdlss Headless 

Hex Hexagon 

In Inch 

I I-Beam 

K. W Kilowatt 

L Angle 



L. H Left hand 

M. S Machine Steel 

M. I Malleable Iron 

Nbr. and No. . . Number 

P Pitch 

Pat Pattern 

PI Plate 

R. and Rad.. . .Radius 

R. P. M Revolutions per minute 

R. H Right hand 

Rd Round 

Req Required 

Sc Screw 

Sq Square 

Std Standard 

T Teeth 

Thd.^ Thread 

V Volt 

W. I Wrought Iron 

W. S Wrought Steel 



Bill of Material. — A device which is known as 
the '^ Bill of Material " is used for listing in table 
form the various items shown on a working drawing. 
This feature which is illustrated in Fig. 78 is gen- 
erally placed upon an assembly drawing, though 
under certain conditions it is made upon a separate 
sheet, given a drawing number, and is included as 
one of a set of drawings. 

The make-up of the bill of material varies with 
the subject matter, but should contain a list of all 
items shown on the drawing, or drawings, as the 
case may be. The name and material of each item, 
the number required, the pattern, tool and drawing 
numbers, usually form the headings for the various 
columns. 

The item number in the bill of material corresponds 
with the number placed on the part indicated; in 



100 PRINCIPLES OF ENGINEERING DRAWING 

this manner each part is Hsted so that the specifica- 
tion clerks may obtain the information which they 
need and there is httle chance for an item to be over- 
looked. The common practice when numbering parts 
is to throw a small circle around the number and to 
connect this circle with the part by means of a 
pointer as indicated in the illustration. Fig. 74. 



Dwg.No.I3625 SiLL OT MATERIAL Sub No. 1 


/tern 
No. 


Descrjption and Mote rial 


Pot. No 


Req. 


© 


B.H.Brockel, C.I. 


N7364 


1 


(D 


B.H. Brocket, C.I. 


r\l 7363 


1 


® 


"^ X 2 i' Taper pm, C.R. 




2 


@ 


{ X l£ 3et 3c. /\^.3. 




4 


@ 


Bushing,! /e cf g X j^ Brass Tubing. 




4 


@ 


lnsBusfiing,3fgofJi X.5I Micoria Tubing. 




4 





Washer, 5^2892, 




4 


® 


fLoc/K iVosner, 5'^5244-0. 




4 


(D 


i X5i Stud, C.R. 




4 


@ 


Washer plate, ireofed F. B .,S*47 2 82 . 




Z 


@ 


Washer plate, fibre, 3*^7281. 




4 


© 


Washer, W. 1. ,5*^72 80. 




4 


@ 


Insu/ofing Cop, 5*4727 8. 




4 


@ 


Washer p/ofe, fibre, 3*47279 . 




4 


© 


Washer plofe, freal-edF.B.,S"^47283 




2 


@ 


B.H.Rod, 8i of /£' Rd.Bn Rod. 




2 



Fig. 78 



Reverse Curves. — It frequently happens that 
certain parts of machines are so shaped that a 
reverse curve is made use of in forming various sur- 
faces. By a reverse curve, we mean a curve formed 
by joining two arcs thrown in opposite directions. 
When this occurs (except for small radii), the radii 
should not touch direct, but should be joined by a 
tangent straight line. This procedure gives a curve 
which is decidedly more pleasing to the eye than 



DRAFTING ROOM CONVENTIONS 101 

would have been the case had the radii been joined 
without the tangent straight Hne. 

Checking. — After a working drawing is com- 
pleted, but before prints of it are sent to the shop, 
this drawing must pass through the hands of an 
individual whose duty it is to catch all errors of 
omission and commission. This individual, known 
as a ^^ checker," studies the drawing in an imper- 
sonal fashion and endeavors to find each fault and 
have it corrected, for if drawings were to reach the 
shop without this procedure many more costly mis- 
takes would be made, as it seems to be nearly im- 
possible for a draftsman to properly check his own 
drawings. 



CHAPTER XI 

WORKING DRAWINGS 

Working Drawings. — In view of the information 
given in the preceding chapter on Drafting Room 
Conventions it should not be necessary to enter into 
much detail upon the subject of our present chapter, 
Working Drawings. There are, however, several ad- 
ditional features which should be mentioned before 
we take up the problems which will follow. 

Working drawings consist in the main of detail 
and assembly drawings. The former, as the name 
implies, is a working drawdng from which the shop 
men produce the parts or details of some mechanism. 
An assembly drawing shows the parts assembled 
together and is used mainly as a guide for the shop 
assembling department, though for certain classes 
of work, assembly drawings are used also as the 
production drawings for some of the parts shown on 
the assembly. 

It is a custom in most plants which produce some 
form of machinery to divide these machines into 
sections. This division is a great convenience in 
the drafting room and is often made use of in the 
shop as an aid in production, by having departments 
which produce only their section of the machines. 

We may illustrate this custom by means of an 
engine lathe which is usually divided into the fol- 



WORKING DRAWINGS 103 

lowing sections: Headstock, Tailstock, Compound 
Rest, Carriage, Apron, Bed and Legs, drawings 
of these sections being grouped under the heading of 
the section as detail or assembly drawings. 

Scale. — When planning a drawing one of the 
first points which it is necessary to settle is the 
" scale " or size we shall make our layout. Gen- 
erally we make drawings to as large a scale as may 
be desirable to show clearly the details of the object, 
always keeping in mind the necessity to show the 
dimensions to good advantage. 

For drawings of machinery in general, the scales 
used are based upon the inch, and those in most 
common use are: full size, | size and J size. For 
buildings, bridges, and very large machinery, the 
scale is based upon the foot, and is usually indicated 
as i' = r, 3'^ = r, etc. 

By either method, the student should persistently 
endeavor to learn to read the different scales by 
eye and should not determine the proportions of the 
figure he is drawing by mathematical calculations. 
If the eye is trained to locate any dimension upon 
the scale (rule), regardless of whether the student is 
drawing full or quarter size, the chances for error 
are greatly decreased, for the eye may be trained 
to detect error before even the mind has quite 
grasped what the error is. 

Titles. — Working drawings are usually identified 
by means of the title and the drawing number, both 
means being especially needed in keeping the records 
of a drafting room. The title is generally placed 
in the lower-right hand corner of the drawing sheet 



104 PRINCIPLES OF ENGINEERING DRAWING 



and usually contains the firm name and address, a 
name which indicates the subject matter of the 
drawing, a drawing number, the scale the drawing 
has been made, and in addition some provision for 
keeping a record of changes, etc. 

At Fig. 79 is shown a standard title and record 







WE5TINIGH0USE ELECTRICa^MFG.CQ 

PITTSBURGH, PA, U.S.A. 

300KW,DCETGEN.,250-500V.5P. 200 RPM. 

BRUSH HOLDER BRACKET 
ruLLSfZE 136255 


yVas CD Ske/chPOOO 
/fem S PaA A/.73e< 
tms cf/ffsren-^. 
Bess af rod en</ 
^vas nof reinforced . 

136255 


— ^ Date- Mar ^3, 05. 
Checked b^ O ^z^ 
/r^sulafion Apfid G^S" 
Design y^pp'<d ^^ 


136255 



Fig. 79 

strip of a well-known firm, which design has proven 
highly satisfactory after many years of experience 
with thousands of drawings in use. 

For the working drawings which follow it is sug- 
gested that we use a title strip similar to that shown 
in Fig. 80, as this is a simple form and contains all 
the information needed for our purpose while leaving 
the body of the sheet free for the drawing. 



NAMC 



SCCTlOhl 
OATC 



Namc or Collcge: 



Title: 

SCALC Dwo.Na 



Fig. 80 

In the case of each assembly drawing among the 
following problems, the student is expected to prepare 
a bill of material to be placed upon these drawings. 
Where the same pattern may be used for the halves 
of a casting, do not fail to use it, but in case the 
halves are to be finished in a slightly different man- 



WORKING DRAWINGS 



105 



ner, they should have separate item numbers. Do 
not overlook any items but see that each part is 
numbered and listed. 

Problems. — Make a working detail drawing from 
the clamp sketch of Fig. 31 in Chapter No. VI. 
Scale, full size. Title, Clamp. 

Make a detail drawing from the sketch of the 




Fig. 81 

shaft support, Fig. 32 Chapter No. AT. Scale, full 
size. Title, Shaft Support. 

Make a detail drawing from the sketch of the tool 
rest. Fig. 33 Chapter No. VI. Scale, full size. Title, 
Tool Rest. 

Make a detail drawing from the pulley sketch 
of Chapter No. VI. This drawing to show a side 



106 PRINCIPLES OF ENGINEERING DRAWING 



view and a sectional view, the latter to be made in 
accordance with the conventional method customary 
for subjects of this type. Scale, J size. Title, 14'' 
Pulley. 
Make a detail dramng of the hand wheel shown in 





hf^iH 



8 Thds.per in. U.S.Sfd. 




2 Grooves fgXj.^ equally spaced. 



Fig. 82 



Fig. 81. Scale, full size. Title, 10'' Hand Wheel. 

From the sketches shown in Fig. 82 make a work- 
ing drawing which includes both details and an 
assembly of this screw jack. Scale, full size. Title, 
Screw Jack. 



WORKING DRAWINGS 



107 




CO 
00 

6 



108 PRINCIPLES OF ENGINEERING DRAWING 

From the sketch illustrated in Fig. 83 make an 
assembly drawing of the coupling. The bill of 
material should include each item shown except the 
portions of the shafts. Scale, full size. Title, Safety 
Flange Coupling. 

From the sketch illustrated in Fig. 84 make an 
assembly dramng of the couphng. It is expected 
that the student will not copy the views as they are 
shown, but will lay them out as follows: Section A-B, 
to be shown as at present, except that the view is 
to be revolved on its axis (clockwise) 90 degrees or one- 
fourth turn, bringing the bolts horizontal, with the 
nuts on the right-hand side. This change in Sec- 
tion A-B will necessitate the lengthwise view being 
revolved on its axis one-fourth turn toward us, bring- 
ing the ends of the nuts on all six bolts into view. 
Scale, J size. Title, Compression Shaft Coupling. 

Make a detail drawing of the lathe leg shown in 
Fig. 85. Scale, \ size. Title, 12'' Speed Lathe — Leg 
Details. 

Make a detail dramng of the bed shown in Fig. 
86. Scale, J size. Title, 12" Speed Lathe — Bed 
Details. 

Make a detail drawing of the rest details shown 
in Fig. 87. Scale, ^ and full size. Title, 12" Speed 
Lathe — Tool Rest Details. 

From the details shown in Figs. 87 and 88, make 
an assembly drawing. Scale, \ size. Title, \2" 
Speed Lathe — Tool Rest Assembly. 

Make a detail drawing of the details shown in 
Fig. 89. Scale, full size. Title, 12'' Speed Lathe — 
Tailstock Details. 



WORKING DRAWINGS 



109 



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110 PKINCIPLES OF ENGINEERING DRAWING 



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WORKING DRAWINGS 



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112 PRINCIPLES OF ENGINEERING DRAWING 




WORKING DRAWINGS 



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114 PRINCIPLES OF ENGINEERING DRAWING 



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116 PRINCIPLES OF ENGINEERING DRAWING 




WORKING DRAWINGS 



117 




OS 

6 



118 PRINCIPLES OF ENGINEEHIXG DRAWING 




K/' 



WORKING DRAWINGS 119 

Make a detail drawing of the details shown in 
Fig. 90. Title, 12'^ Speed Lathe — Tailstock Details. 

From the details shown in Figs. 89, 90 and 91, 
make an assembly drawing. Scale, ^ size. Title, 
12'^ Speed Lathe — Tailstock Assembly. 

Make a detail drawing of the details shown in 
Fig. 92. Scale, J size. Title, 12'' Speed Lathe — 
Headstock Details. 

From the details shown in Figs. 92 and 93, make 
an assembly drawing. Scale, ^ size. Title, 12'' 
Speed Lathe, Headstock Assembly. 

From all of the speed lathe details shown from 
Figs. 85 to 93, inclusive, make a general as- 
sembly of this machine. This drawing should be 
placed on an A size sheet (22'' x 30") and two views 
shown, the front and the headstock end, preferably. 
Scale, J size. Title, 12" Speed Lathe Assembly. 



CHAPTER XII 

TRACING AND BLUE PRINTING 

Ruling Pen. — When learning to trace, one of the 
first difficulties encountered is the proper method of 
handling the ruling pen and compass. 

In general, the ruling pen and the pen point of 

the compass should be held in such a manner as 

to bring the points of both jaws on the paper at 

the same time, as shown at (6) of the illustration, 

Fig. 94. Do not lean the pen either toward the 

ruling edge or away from it, but hold it in a vertical 

plane, for it is only w^hen a pen is held thus, that 

sharp, even lines, free from a ragged edge, can be 
produced. 

While the pen should not be leaned toward or 
away from the ruling edge, it will be found that the 
ink will flow more freely if the pen is leaned slightly 
in the direction in which the line is being ruled, as 
indicated at (a) in Fig. 94. 

In Chapter No. II, mention was made of the 
proper method of ruling vertical lines by means of 
the T square and the left-hand edge of the triangle. 
This admonition is especially necessary when ruling 
these lines in ink, for it is very desirable to hold the 
ruling pen in an easy, natural manner, one in which 
the point of the pen is clearly in sight at all times. 

A common mistake of most beginners is to fill the 
pen with too much ink, with the result that, before 



TRACING AND BLUE PRINTING 



121 



they realize it, there is a big smear on their work. 
This is not necessarily caused by the pen being filled 
too full, but it is frequently the cause. It is better 
to fill the pen oftener and to use less ink at one 
time. Another excellent habit to acquire is to wipe 
out the pen each time fresh ink is put in, as the ink 
flows more freely from a clean pen than from a 
dirty one. 

Tracing Cloth. — Tracing cloth is a fine linen 
fabric so prepared that it is transparent, with one 




1 



a 



Fig. 94 



side glossy and the other dull. The dull side is 
the one most popular with draftsmen, prob- 
ably due to the fact that it takes both pencil and 
ink more freely than the glossy side. Ink erasures 
may be made more easily on the glossy side as the 
ink does not sink in so deeply as on the dull 
side, the wax-like preparation tending to carry the 
ink on the surface. 

Owing to the sizing material with which tracing 



122 PRINCIPLES OF ENGINEERING DRAWING 

cloth is treated, it is necessary to prepare it for use 
b}' rubbing chalk dust or talcum powder over the 
surface before the ink will take hold. Care should 
be taken to wipe off this powder after rubbing it in 
well, as an excess amount left on the surface tends 
to clog the ruling pens. 

Old tracing cloth or sheets that have been spoiled, 
if washed out, make the best of pen wipers and rags 
to use in keeping the triangles and the T square 
wiped clean. 

Tracing. — When beginning a tracing, tack the 
cloth down carefully, stretching it tightly over the 
pencil dramng, then prepare the surface with chalk 
as mentioned above, now adjust the compass pen 
to the width of outline desired; do this, by trying 
the compass on a scrap of tracing cloth which has 
been prepared. In deciding on the width of line, 
the student should bear in mind that to get blue- 
prints with clear white lines, it is necessary that the 
lines of the tracing be fairly heavy; not the fine 
thin lines that beginners are so prone to use. 

The illustration, Fig. 95, shows the various steps 
in making a tracing: First, throw in all the circles 
and radii; then, beginning at the top, rule in all 
the horizontal outlines; next, starting at the left 
side, rule in all the vertical outhnes; and, finally, 
rule in the angular outlines. 

Now, adjusting the pen to a much finer Kne, or 
using the small pen so adjusted, rule in the pro- 
jection lines; these lines for drawings of small figures 
should be composed of dashes from i to | inch long, and 
for large figures from J to f inch long. Do not let the 



TRACING AND BLUE PRINTING 



123 



projection lines touch the figure, but leave a slight 
opening between the end of the line and the figure. 

Next, rule in the dimension lines; these lines for 
drawings of small figures should be solid except for 
the opening left for the dimension, but on drawings 
of large figures they may be broken lines of long 
dashes, the length to suit the size of the drawing. 



') 



l5t. Circles and Radii 







5rd. Vertical lines 





2nd. Horizontal lines 

Dimension lines 



4 til. Angular lines 

Projection lines 




eThdper in. 

5th. Projection and Dimension lines^ 

Dimensions^ Notes 
Fig. 95 

Now, place the arrow-heads on the dimension 
fines and put in the dimensions, using care to make 
the figures clear and distinct; and, finally, if there 
is a sectional view, rule in the section fines, leaving 
an opening around dimensions where they occur in 
the sectioned part. To get the effect of contrast the 
section lines should be even lighter than the dimen- 
sion lines. 



124 PRINCIPLES OF ENGINEERING DRAWING 

Finished Tracing. — In the finished tracing there 
should be a marked contrast between the weight of 
the outhnes of the figure, and of the center, pro- 
jection, and dimension lines; the latter should be 
decidedly lighter than the outlines. When these 
various lines are drawn to the proper proportions 
and are well arranged, the figure seems to stand out 
by itself and is much more easily understood. 

When the tracing is otherwise completed, print all 
notes and the title on carefully and neatly, as the 
appearance of a good drawing will be spoiled if the 
lettering is done in a careless, slipshod manner. 

General Notes. — When the student attempts to 
letter with ink for the first time, he will discover 
that it is quite a different matter from lettering with 
a pencil. Lack of confidence and a pen point not 
yet properly broken in, are the major difficulties 
which he must overcome, and there is just one means 
of doing this — intelligent practice. 

Guide lines on the pencil drawing that ma}" be 
seen clearly through the tracing cloth, or light pencil 
guide lines on the tracing itself are very helpful in 
producing letters of uniform appearance. 

Pen points of various makes are in use but one 
of the best for dimensioning tracings, and for all 
lower case lettering, is the Gillott No. 303. The 
De Haan double spring No. 16 is an excellent point 
for titles and headings where capitals are used. 

Erasures on tracings require care and patience 
and while this is a necessary feature of the work 
it is a very unpopular one in drafting rooms. Where 
it is necessary to take out lines or smear marks, 



TRACING AND BLUE PRINTING 125 

use an ink eraser, not a pen-knife, as the latter in 
the hands of a novice will do more harm than good. 
An erasing shield is useful in protecting the part 
which is to be maintained. 

After an erasure is completed, when new lines 
are to be inked in on this surface, this part of the 
tracing should be rubbed with a stick of talc (tailor's 
chalk) as this properly prepares the destroyed sur- 
face to take ink once more. If this is not done the 
ink is apt to spread and cause an ugly looking patch 
on the tracing. 

Do not let any water drop on your tracing as the 
effect would be similar to that made on a starched collar. 

To clean pencil marks from tracings, some of the 
soft rubbers are excellent, but to remove dirt and 
stains from a tracing that has been handled a good 
deal, use a piece of soft cotton waste soaked in 
benzine or gasoline as neither affects the ink and 
both evaporate quickly. 

Blue Printing. — The tracing represents the fin- 
ished record of a design which must be carefully 
preserved from destruction. An almost unlimited 
number of copies of this tracing may be made in 
the form of blue prints which are sent into the shops 
for use in the production of the mechanism illus- 
trated by the drawing. 

These blue prints are comparable to prints made 
from a photographic negative and are printed in very 
similar fashion, due allowance being made for the 
difference in methods of handling. 

Paper. — The surface of a white paper is pre- 
pared by coating it with a chemical solution which 



126 PRINCIPLES OF ENGINEERING DRAWING 

is affected by light; consequenth^ this sensitized paj^er 
must be handled in a room where the light is not 
sufficiently bright to spoil it. When exposed to 
hght the chemical action is such that the sensitized 
surface turns to a dark blue color when the print 
has been thoroughly washed in water. 

Prepared blue print paper of various sizes and 
weights may be purchased in rolls and if properly 
protected from the light may be kept for a reasonable 
length of time without deterioration. 

Printing. — The simplest form of blue-print frame 
which is used with sunlight is identical with that 
used for photographic printing except as to size. 
In large plants it is not possible, owing to the amount 
of work to be done, to depend upon sunlight; as a 
consequence, electric printing and washing machines 
have here replaced the old methods. 

To make a blue print in a simple frame, place the 
tracing in the printing frame, ink side next to the 
glass, cover this with a sheet of prepared paper 
with the sensitized surface on the tracing; now 
clamp down tightly the padded back so as to hold 
the tracing and the print paper perfectly flat; if this 
is done, when the exposure is made, the light will 
strike all of the sensitized surface of the paper 
except where the ink lines intervene. After an ex- 
posure of a few minutes the print is placed in a water 
bath and the solution not affected by the light is 
thoroughly washed out. The result is a sheet with 
the ink lines of the tracing reproduced in white 
upon a dark blue background. After the print is 
thoroughly dry it is ready for use. 



TRACING AND BLUE PRINTING 127 

Van Dyke Prints. — Van Dyke paper prints or 
^^ Brownies/' as they are frequently termed, are a 
convenience for certain purposes on account of their 
brown color and the texture of the sensitized paper 
which will take ink if carefully applied. 

These Brownie prints are made in the same manner 
as blue prints, except that for certain grades of paper 
it is necessary to ^^ fix " the prints in a ^^ hypo " 
bath as photographic prints are treated. 

As the nickname implies this print is of a dark 
brown color with white Hues, and if we use one of 
these prints as a negative we obtain white prints 
with brownish black lines. These white prints are 
very convenient for sketching in changes of design, 
after which the print may be used as a guide when 
changing the original tracing. 

In most drafting rooms, situations arise that neces- 
sitate preparing a special drawing on short notice, 
a drawing which may be used for the emergency 
only and then is filed away as a record. Many of 
these emergency drawings are for special orders 
which do not allow the time necessary to prepare 
new drawings, orders that would necessitate changing 
an original drawing or the production of a new one 
from the old, with the special features incorporated. 

With the use of Van Dyke paper we may take a 
strong brown print from the original tracing above 
mentioned, but, instead of erasing the part to be 
changed on the original tracing, we cover with draw- 
ing ink the white lines of this part on the Brownie, 
and from this negative produce a white print. The 
part to be altered having been blocked out, is shown 



128 PRINCIPLES OF ENGINEERING DRAWING 

in white, the special order change is penciled and then 
inked in on this print which, when complete, is used 
as an original drawing from which we may obtain 
blue prints to produce the special order. 



CHAPTER XIII 
Reference Tables 

Under the head of Standard Data in the chapter 
on Drafting Room Conventions, mention was made 
of the use of reference matter as an aid to draftsmen. 
In choosing the various data sheets which fohow we 
have tried to furnish only such reference matter as the 
student is apt to need frequently in handling the work 
of this text and later when taking up problems in 
design. 

Where a definite standard has been established along 
the lines of the reference matter of these sheets, we 
have made use of it; but where no such universal 
standard has been developed we have used the stan- 
dards of certain well known manufacturers. 

In using these reference tables the student should 
become familiar with the custom practiced in com- 
mercial drafting rooms in such matters, for there^ 
there is no occasion to waste time in calculating the 
sizes of certain standard details of design; instead, 
this information is obtained from the company's 
standard sheets which are usually prepared by a 
portion of the engineering department organization. 

The form in which this reference matter is usually 
presented is largely a matter of taste in conjunction 



130 REFERENCE TABLES 

with the restrictions made b}^ the size of the standard 
sheet, but the material itself has been carefully deter- 
mined by some of the best engineering minds of the 
country and may be accepted as representing the 
mass judgment of the engineering world. 











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National. Tubc Companv Standa-rd 


Sii£ 
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Diameters, 
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W&igh t per f oof. 
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Couplings 


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2 7/7 

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2.731 
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5.793 


5.819 


8 


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3.500 3 068 


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7.575 


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7.625 1.023 


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The permissible variation in t^eighl- is -3 per cenf above and S per cen-h 
beloy/. Furnished yyifh threads and couplings and in random l&ngfhs 
unless otherwise ordered Taper of threads is ^ diamet'er per Foot 
length for all sizes. The ir^ eight per fooi of pipe yvith threads and 
couplings is based on a length of 20 feet, including the coupling , but 
shipping lengths of small sizes vrill usually average /ess than 20 feet 

All yveights and dimensions are nominal. On sizes made m more than 
one yveiahfj neighi desired must be specified. 



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